Since it was first identified at the end of 2019, the novel coronavirus has brought about a whole new way of life for most of us, and with that, a new vocabulary. It's critical to understand what the experts recommend and why so that we can all follow guidelines to keep us and everyone around us safe.

If reading updates about COVID-19 often has you searching for an (online!) dictionary, here’s a quick rundown of all the most common terms and what they mean in relation to the virus.

Antibodies An antibody is a blood protein that the immune system makes as a response to an invader (pathogen), such as a virus. Antibodies are unique to a particular pathogen; when a person has antibodies for the infection caused by the coronavirus that causes COVID-19, called SARS-CoV-2, it means that the person has been exposed to the virus and the body has mounted an immune response.

Research is ongoing about whether people with coronavirus antibodies have any protection against getting COVID-19 again, at least for a certain amount of time, as has been the case with other viral illnesses. The World Health Organization (WHO) has stated that the assumption of immunity won't be proved until researchers are able to study people who have contracted and recovered from the virus for longer periods.

Community spread Community spread means people have been infected with the coronavirus in an area, says the Centers for Disease Control and Prevention (CDC), including some who don’t know how or where they became infected.

Community spread is hard to contain, particularly because experts believe that many people with the coronavirus can be asymptomatic or pre-symptomatic but can still infect others. Currently, the best way to prevent community spread is by avoiding crowds, staying home as much as possible, and staying at least six feet apart from other people.

Containment Containment strategies are used at the beginning of an outbreak. It helps officials track the spread of the virus or disease within a community and then uses isolation or quarantines to keep those infected individuals from spreading the disease to other people.

Using containment strategies in conjunction with other measures like physical distancing can help limit the number of cases of a disease, especially if the actions are taken soon after the outbreak is recognized.

COVID-19 COVID-19, also called coronavirus disease 2019, is the respiratory disease caused by SARS-CoV-2, the technical name for the new coronavirus. COVID-19 is part of a family of coronavirus diseases that include the common cold, SARS, and MERS.

COVID-19 was first reported at the end of 2019 in Wuhan, China, and the first confirmed case in the United States was on January 2, 2020, in Washington state.

Symptoms of COVID-19 include fever, cough, and shortness of breath, though the majority of people who become infected have only mild symptoms.

COVID pneumonia A complication of COVID-19 infection, this is a lung infection in which inflammation causes air sacs in the lungs to fill with fluid or pus. Ultimately this causes hypoxemia (low blood oxygen levels).

Hypoxemia can cause organs to malfunction, and in severe cases can interfere with brain or heart function. It’s possible to have advanced pneumonia without experiencing difficulty breathing, a condition called “silent hypoxia.”

COVID toes Red or purple bumps may appear on the toes of some people who contract COVID-19, known as COVID toes. It isn’t uncommon for people battling a viral infection such as COVID-19 to have a rash or blotchy areas on their body; COVID toes can be one manifestation of that. The bumps can appear on the toes or the hands and feel itchy, burning, and painful.

Although COVID toes have been observed in many patients with the coronavirus, they are much less common than typical COVID-19 symptoms such as cough, shortness of breath, and fever.

Epidemic COVID-19 was declared an epidemic before it was a pandemic. An epidemic occurs when a disease rapidly spreads to a large number of people within a community, population, or region. An epidemic is a sudden increase in the number of cases of a disease — above what would normally be expected. The term “outbreak” has the same definition, though experts often use this term when the geographic area is smaller.

Examples of epidemics or outbreaks would be the Zika virus in 2016 on the continents of Africa, the Americas, Southeast Asia, and the Western Pacific, according to the WHO, and the Ebola virus in West Africa.

Fatality rate Also called fatality risk, this is the percentage of people who die from a disease compared with the total number of people who were diagnosed with the disease in a certain time frame.

Originally experts thought the fatality rate for the coronavirus was between 2 and 3.4 percent, but a study published on Thursday, March 19, in Nature Medicine reported that people who had the coronavirus symptoms in Wuhan, China, where the virus began, had a 1.4 percent chance of dying.

Flattening the curve When viewed on a graph, a sudden surge in people getting sick with COVID-19 over a very short period (within a few days) can look like a tall, narrow curve, similar to a spike. This type of surge happened with the coronavirus in Italy, and the number of people who were sick and needed hospitalization overwhelmed the healthcare facilities, safety equipment, and healthcare providers.

The United States and countries around the world want to “flatten the curve” if possible, meaning that a smaller number of people are sick with coronavirus at any one time. Fewer people will die of COVID-19 if we are able to slow down the spread of the disease through measures like physical distancing and isolation.

Herd immunity Herd immunity is an indirect form of protection from an infectious disease that occurs when a certain percentage of the population becomes immune, either because they’ve been ill and recovered or because they’ve been vaccinated.

When COVID-19 first appeared, no one was immune because it was a new virus — allowing it to spread quickly from person to person.

Achieving herd immunity against COVID-19 in the United States will require up to 70 percent of the population to have recovered from the disease or received a vaccine, according to the Mayo Clinic. Currently, there is no vaccine for COVID-19.

When herd immunity is achieved for a disease, it can help protect vulnerable people from contracting it. Chicken pox, measles, and polio are examples of diseases that were once common but are now rare because of vaccination.

Immunocompromised People who are immunocompromised have a weakened immune system, meaning their white-blood-cell counts are low or they have other conditions that make it harder to fight off infections and diseases. Examples of people who are immunocompromised include cancer and transplant patients who are taking certain immunosuppressive drugs, people living with HIV/AIDS, and people with inherited or acquired diseases that affect the immune system (including but not limited to diabetes, rheumatoid arthritis, and lupus).

People who are immunocompromised are at higher risk for severe illness from COVID-19. It’s recommended that this group continue taking any medications for their underlying condition and stay on their treatment plan unless directed by their doctor to do otherwise. Immunocompromised individuals should not delay getting emergency care for their underlying condition because of the virus, according to the CDC.

Incidence Incidence refers to the number of individuals who develop a specific disease or illness (like COVID-19) during a given period of time, according to the CDC. The incidence rate is the number of new cases of a disease existing in a population at a specific time divided by the total number of people at risk for that disease in that population.

Monitoring changes in incidence in different areas is important for experts to understand community spread and what types of social distancing measures need to be in place.

Incubation The period between when a person is first exposed to a virus and when they develop symptoms is known as the incubation period. Knowing the incubation period for the coronavirus can help experts know when the disease can be spread, even if a person is without symptoms.

Intubation This is a medical procedure that may be used for people with severe COVID-19 who are unable to breathe on their own. A flexible plastic tube (a breathing tube) is inserted through the mouth into the trachea, the large airway from the mouth to the lungs. The tube is then connected to a machine called a ventilator that can move air to and from the lungs.

Medical staff will administer a sedative before intubation to relax the muscles around a patient’s throat, preventing the person from gagging or trying to pull the tube out.

Isolation If a person has a confirmed case of coronavirus, they are instructed to practice isolation, which may be at home or in the hospital, depending on how sick the person is. It’s meant to keep sick people from infecting other people by keeping them away from everyone.

Because the disease is spread by tiny droplets in the air, healthcare workers wear masks and protective equipment to care for people in isolation. The CDC recommends that patients in isolation at the hospital should have their own single room with the door closed and their own dedicated bathroom.

For people in isolation at home, they should wear a mask when other people are present and sleep in a separate bedroom and use a separate bathroom if possible. Door handles, taps, and common surfaces should be cleaned daily with disinfectant.

Middle East respiratory syndrome (MERS) First identified in Saudi Arabia in 2012, MERS is a zoonotic virus, meaning it’s thought that humans caught MERS from animals, in this case camels. It’s not very easily transmitted from person to person, and human transmission has been limited; but it is deadly. So far, 2,494 cases of MERS have resulted in 858 deaths.

Mortality and morbidity Mortality is another word for death. The mortality rate measures how many people die in a defined group or population (such as a city or a country) during a specified time period. The deaths are often measured per 1,000 or 100,000 people. For example, if there were 60 deaths in one year in a population of 30,000, then the mortality rate would be 200 per 100,000.

Morbidity means illness, and one person can have several comorbidities at the same time. The morbidity rate is often mathematically calculated as the mortality rate, but it measures illness rather than death.

Pandemic COVID-19 was declared a pandemic by the WHO on March 11, 2020, making it the first time in history that a coronavirus caused such an event. A pandemic is the global outbreak of a disease; pandemics are usually classified as epidemics first, which is when a disease is spreading rapidly in a particular area or region. The opioid epidemic in the United States or Ebola in West Africa in 2014 are examples of recent epidemics.

According to a statement posted by the WHO's director-general on March 11, the decision to call the coronavirus a pandemic was made because “we are deeply concerned both by the alarming levels of spread and severity, and by the alarming levels of inaction.” At the time of the announcement, the virus had spread into six continents and more than 100 countries.

Physical distancing or social distancing Physical distancing, commonly referred to as social distancing, is the deliberate increase of physical space between people to keep them from spreading illness. Experts recommend staying at least six feet away from other people to reduce your risk of catching the coronavirus.

Mental health experts recommend using the more precise term "physical distancing" because, according to an article published March 21 by CNN, when practicing keeping a physical distance, social connectivity is critical.

Public gatherings like conferences, concerts, and sporting events have been canceled because of physical distancing recommendations. Schools around the country have canceled classes, and most people are being encouraged to work from home if possible.

PPE or personal protective equipment Personal protective equipment or PPE is equipment worn by healthcare workers to reduce exposure to the coronavirus. The CDC recommends that those caring for people with COVID-19 wear goggles or a disposable full-face shield, a respirator known as an N95 mask, a gown that covers their clothes, and clean gloves.

This gear is necessary to help prevent healthcare workers from becoming infected with the virus and spreading it to their colleagues or other patients. Hospitals across the United States, particularly in areas hard hit by the virus, have been struggling with PPE shortages since the beginning of the pandemic.

Proning This is the practice of repositioning a patient in their hospital bed so they’re lying on their stomach or on their side rather than on their back. Doctors have discovered that for patients with COVID-19, redistributing body weight this way can improve oxygen saturation levels by “opening up” parts of the lung, in many cases reducing the need for a ventilator.

Respirator A respirator is a device that protects a person from inhaling dangerous substances such as chemicals or infectious particles. The type of respirator most typically used to protect against COVID-19 is commonly known as an N95 mask, which can filter out small viral particles from the air. A shortage of N95 masks has been one of the many challenges facing healthcare workers in the United States.

R-naught or R0 Every virus has a basic reproduction number (R0). The R0 (pronounced R-naught) is the average number of additional people that one person with the virus will infect. That number depends not only on how transmissible the virus is, but also how easy or difficult the behavior of the community makes it for the virus to spread. Estimates published in Nature on March 18 suggest the R0 of COVID-19 is between 2 and 2.5.

A higher R0 doesn’t necessarily mean a worse disease. Seasonal flu has an R0 of 1.3 yet affects millions of people every year; SARS had an R0 between 2 and 5 but infected only around 8,000 people total.

Self-quarantine Given the incubation period, it’s not always easy to know if and when exposure to the coronavirus has occurred. If a person has returned from travel to a high-risk area or has been exposed to someone who has tested positive for the new coronavirus, the CDC recommend that they self-quarantine for 14 days.

The quarantine period restricts the movement of the person (even though they may not seem sick or actually be sick) until the incubation period is over to see if they become ill. Self-quarantine can go a long way in limiting the spread of a communicable disease such as COVID-19. Staying at home is the first step of self-quarantine, but it also involves other important behavioral changes, according to the CDC, which include:

No visitors
No sharing towels or utensils
Washing hands frequently
Practicing physical distancing by staying at least six feet away from other people in your household

Severe acute respiratory syndrome (SARS) This viral respiratory coronavirus began in Asia in 2003 and spread to 29 countries. Most people with SARS start feeling ill with a fever, chills, and body aches, and then develop pneumonia. A total of 8,096 people were infected with SARS, and 774 people died as a result of the illness. Containment efforts were successful and there have been no reported cases of the virus since 2004.

State of emergency The U.S. government declared a state of emergency in order to try to contain the coronavirus on Friday, March 13, as reported in an article by ABC News. This is different from the “public health” emergency that was issued by the Health and Human Services (HHS) secretary Alex Azar at the end of January, which was made to help state agencies redirect funds and staff to address COVID-19.

Trump declared a national emergency with the Stafford Act, often used for natural disasters like floods or tornado damage, and it allows billions of dollars in Federal Emergency Management Agency funds to be funneled into efforts to battle the coronavirus.

An emergency was also invoked under the National Emergencies Act, which allows HHS to modify or relax regulations for national healthcare programs like Medicare and Medicaid as well as hospitals. Examples include provisions so that healthcare providers can do consultations by phone and patient-capacity limits for hospital can be temporarily waived.

Ventilator This is a machine that takes over the breathing process when patients can’t breathe well enough on their own (respiratory failure), causing a buildup of carbon dioxide in the blood that can lead to organ damage.

There are two kinds of medical ventilators. One is more invasive and requires sedation and a tube inserted into the airway (called intubation) that pushes a mixture of air and oxygen into the lungs. The other is noninvasive and uses a face mask, nasal mask, or a mouthpiece to deliver oxygen.

People with COVID-19 may be placed on a ventilator if the amount of oxygen in their blood (oxygen saturation level) dips below a certain threshold.