Coronavirus: Glossary of Common Terms

Medically Reviewed by Dan Brennan, MD on January 03, 2023
8 min read

Use this glossary to get familiar with terms often used in coverage of the novel coronavirus, which causes COVID-19.

Aerosol: A tiny particle or droplet that’s suspended in the air.

Antibody: A protein your immune system makes in response to an infection. If you have antibodies for the coronavirus in your blood, it means you have been vaccinated or infected with this virus at some point (even if you never had any symptoms).

Antibody test: Also called a serology test, this checks to see if you have antibodies in your blood that show that you were previously infected with the virus.

Antigen test: A type of diagnostic test that checks to see if you're currently infected. The test looks for proteins (antigens) in a sample taken from your nose or throat. Antigen tests are faster than PCR tests, but they are less accurate and have a higher risk of false positives (meaning that they’re more likely to say you have the infection when you don’t) and false negatives (meaning they’re more likely to say you don’t have the infection when you do). This may also be called a rapid test or rapid diagnostic test.

Asymptomatic: Lack of symptoms. It is possible to contract the coronavirus and make antibodies to it even if you stay asymptomatic. It is also possible to spread the virus to others if you're carrying it but have no symptoms.

Booster. A vaccination given after a previous vaccination in order to boost the protection offered by the previous shot.

Cluster: A grouping of disease cases in a geographic area during a set time period.

Contact tracing: A disease control measure. Public health workers known as contact tracers work with infected people to identify anyone they had close contact with while they were contagious. The exposed contacts are then informed that they might be carrying the coronavirus. Recommendations to quarantine, get tested, and wear well-fitting masks depend on their vaccination status and whether they’ve had a COVID-19 diagnosis within the past 90 days.

Convalescent plasma therapy: A treatment that involves taking blood from someone who has antibodies to a disease, separating out the clear liquid part (plasma), and then giving it to someone who is sick with the same illness. This technique has been used to treat many different diseases but is still considered experimental for treating COVID-19. The World Health Organization does not recommend its use for milder cases of COVID-19. The WHO says it should only be used within clinical trials for severe and critical COVID-19 patients.

Coronavirus: A type of virus that looks like a corona (crown) when viewed under a microscope. There are many different coronaviruses. Most cause mild respiratory infections like the common cold, but others can cause serious illness. The strain of coronavirus that is causing the COVID-19 pandemic is called SARS-CoV-2.

COVID-19: Stands for coronavirus disease-19. COVID-19 is the name of the infection caused by the novel (new) strain of highly contagious coronavirus (SARS-CoV-2) that was first identified in late 2019.

Diagnostic test: A test that checks to see if you are infected. This is usually done via a swab test, which entails taking a sample from the back of your nasal cavity so it can be analyzed in a lab to see if it contains genetic material from the virus. This test may use a saliva sample instead. It’s also called a viral test.

Drive-thru testing: Instead of visiting a doctor's office or other indoor health care facility, patients pull up in their cars to a specific outdoor site where diagnostic and/or antibody tests for COVID-19 are done. Health care providers stand outside and do testing through car windows.

Droplet: A tiny moist particle that is released when you cough or sneeze. You may get the coronavirus if you’re close to someone who is carrying it and your mouth, nose, or eyes come into contact with droplets they have released.

Emergency use authorization: A ruling put out by the FDA in an emergency, allowing medical professionals to use certain products before they have the agency’s full approval, clearance, or licensing.

Endemic: The baseline or expected level of a disease in a given community.

Epidemic: A significant and possibly sudden increase in the number of cases of a disease in the community.

Flattening the curve: Refers to efforts designed to prevent too many people from getting sick around the same time, which would overwhelm the health care system.

Herd immunity: When the majority of people in an area are immune to a specific infection, even the members of the population (herd) are protected simply by being around them. 

Hydroxychloroquine: A medication used to treat or prevent malaria. The FDA originally granted emergency use to treat patients with COVID-19 based on very limited data showing that it has activity against SARS-CoV-2. But the ruling was later removed because studies didn’t show that the drugs worked against COVID-19 or that its benefits outweigh the risks.

Incubation period:­ The time from when you're exposed to an infectious disease to when you get symptoms. The incubation period for COVID-19 is usually between 2 and 14 days, with the midpoint being 5 days.

Infusion: A procedure that puts a medicine, blood, or fluid directly into your veins through an IV or catheter over a period of time.

Monoclonal Antibodies. A type of protein that is made in the laboratory and can target the coronavirus that causes COVID-19 to stop it from spreading. The antibodies are administered through IV injection.

N95 respirator: Unlike a surgical or cloth mask, N95 respirators (sometimes called N95 masks) are designed to prevent the wearer from breathing in tiny particles. When fit properly, they filter out at least 95% of large and small particles.

Outbreak: Similar to an epidemic, but it usually refers to a group of cases within a smaller area.

Pandemic: An epidemic that has spread to several countries or continents.

Paxlovid:  Nirmatrelvir tablets and ritonavir tablets (Paxlovid) is the first oral COVID-19 treatment cleared by the FDA. This antiviral drug from Pfizer treats adults and children 12 and older (weighing at least 88 pounds) who have mild-to-moderate COVID-19 and are at high risk of the disease becoming severe. 

PCR test: Stands for polymerase chain reaction test. This is a diagnostic test that determines if you are infected by analyzing a sample to see if it contains genetic material from the virus.

Personal protective equipment (PPE): Includes N95 respirators as well as gowns and gloves designed to protect health care workers from infectious diseases like COVID-19 while in close contact with patients.

Pre-symptomatic: If you’re pre-symptomatic, you have contracted the virus and may soon feel symptoms, but at the moment, you don't have any. It may be possible to spread COVID-19 to others during this phase.

Quarantine: The practice of staying home and away from others for at least 5 days after you've been exposed to COVID-19 to see if you get symptoms and to avoid spreading the virus if you are carrying it. After you quarantine, get tested at least 5 days after your last contact, even if you don’t have symptoms, and take safety measures until 10 days after you were last exposed to COVID: Watch for symptoms, wear a well-fitting mask (NIOSH-approved N95 respirators offer the most protection), avoid travel, and stay away from people who are at high risk of catching or getting sick from COVID. Isolate right away and get tested if you develop symptoms.

R0: Pronounced r-naught, this is the "basic reproductive number" of a contagious disease: the average number of additional cases that directly result from a single person bringing it into a community. COVID-19 is believed to have an R0 of 2.2-2.7, which means that the first person who has it in a community will likely infect two or three others, and those newly infected people will each go on to infect another two to three people, rapidly spreading the virus.

Remdesivir (Veklury): An antiviral drug made to treat Ebola (but never approved for that purpose), remdesivir is the first treatment to be granted full approval by the FDA to treat COVID-19. Evidence shows that those treated with remdesivir recovered in about 11 days compared to 15 days for those treated with a placebo.

SARS-CoV-2: Stands for severe acute respiratory syndrome coronavirus 2. SARS-CoV-2 is the specific strain of coronavirus that causes the COVID-19 disease.

Self-isolation: Stricter than quarantine, self-isolation refers to staying in a contained area -- perhaps a single room in your home if you don't live alone -- because you have COVID-19 and are trying to avoid infecting others.

Serology test: Also called an antibody test, this checks to see if you have antibodies in your bloodstream that indicate you had been infected with the virus in the past.

Social distancing: The practice of keeping extra space between two people -- 6 feet is the minimum recommended amount -- to prevent spreading the virus. Canceling large gatherings, working at home instead of in an office, and switching from in-person school to remote learning are also parts of social distancing.

State of emergency: A declaration made by the governor of a state because a disaster is occurring or about to occur. Allows the governor to quickly direct funds to protect the public during a crisis.

Swab test: A type of diagnostic test that involves taking samples from the back of your nasal cavity so it can be analyzed in a lab to see if it contains the virus. Also called a viral test.

Tocilizumab (Actemra): an immunosuppressant used to treat rheumatoid arthritis and is being used in trials to treat COVID-19. The coronavirus appears to trigger an overactive immune response in some people, doing a lot of damage to organs and increasing the risk of death. This drug is being used in clinical trials to counter that response.

Trial: Short for a clinical trial, this is when researchers study a medical test or treatment in a set group of people to make sure it’s safe and effective before giving it to the public.

Vaccine: Prevents disease by training your body’s immune system to fight a germ that it’s never come into contact with before.

Variant: A change or alteration in the original. In the case of the coronavirus, a variant is a mutation in which the original virus has taken on new characteristics.

Ventilator: A machine used to pump air into your lungs if they aren't working properly on their own. Someone who requires a ventilator will need to have a tube put into their windpipe (a process called intubation) so the ventilator can be connected to it.

Viral load: Also called viral dose, viral load refers to the amount of virus you are exposed to. Someone who is exposed to a relatively small amount of the coronavirus might not get any symptoms, while someone who is exposed to a large amount is more apt to get severe symptoms.

Viral shedding: The release of virus from an infected person into the environment, where it can infect others. In the case of COVID-19, most viral shedding occurs through the respiratory tract (often via a cough or sneeze), but the virus may also be shed though the gastrointestinal tract and show up in the stool.

Viral test: Also called diagnostic test, this checks to see if the active (live) virus is present in your body. In the case of COVID-19, this usually involves taking a sample from the back of your nasal cavity (swab test) so it can be analyzed in a lab to see if it contains genetic material from the virus.

Virus: A tiny infectious organism made up of genetic material (DNA or RNA) wrapped in a protein coat. Viruses can't multiply on their own; they reproduce by invading living cells and taking control of them.