The COVID-19 dictionary: everything you need to know

Mike Bohl, MD, MPH, ALM - Contributor Avatar

Written by Health Guide Team 

Mike Bohl, MD, MPH, ALM - Contributor Avatar

Written by Health Guide Team 

last updated: Sep 15, 2021

6 min read

Here's what we'll cover

  1. Covid A-Z

Antibodies, incubation, quarantine—who could have imagined these terms would become such common parts of our conversations and lives? The COVID-19 pandemic has changed so much about our day-to-day lives, and the words and phrases we use are no exception. Here’s a dictionary of some of the terms you might have questions about, and what they mean for your life. 


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Covid A-Z

Antibodies. Antibodies (also called immunoglobulins) are an important part of the immune system. When the body is exposed to an infectious agent (such as a virus or bacterium), the body produces antibodies to it. The antibodies then help the body fight the infectious agent. A COVID-19 antibody test (also called a serologic test) is a blood test that looks for antibodies to COVID-19, to see if you have been exposed to the virus in the past.

Asymptomatic. Asymptomatic means having no symptoms. After becoming infected with coronavirus, most people are asymptomatic for several days and some are asymptomatic throughout the entire course of their infection. However, it is important to remember that you can still transmit and spread the virus when you are asymptomatic.

The Centers for Disease Control and Prevention (CDC). A federal agency that was founded in 1946 and is responsible for limiting and preventing disease, injury, and disability in the United States and abroad. For recommendations about the most up-to-date guidelines around the COVID-19 pandemic, consult the CDC’s website.

Community spread. When a disease spreads from person to person in the community. People who are newly infected may not know when or where they were infected. 

Contagious. Able to spread by direct or indirect contact. People can be contagious and transmit the novel coronavirus for days before they show symptoms. People are most contagious before and during the first week of symptoms.

Containment. Limiting the spread of disease to one geographic area. Attempts to contain the virus that causes COVID-19 failed, so it spread internationally.

Coronavirus. A family of viruses named for the distinctive spikes on their surface. Corona means a crown, and the spikes are seen as a crown on the virus surface. Coronaviruses cause a variety of respiratory illnesses, including SARS, MERS, COVID-19, and the common cold.

Coronavirus disease 2019 (COVID-19). COVID-19 is the name of the disease caused by the novel coronavirus SARS-CoV-2. The disease produces mild flu-like symptoms in most cases. In others, it can cause severe symptoms requiring hospitalization. Severe cases may necessitate mechanical ventilation and can even lead to death.

Droplets. Respiratory droplets are produced when a person coughs or sneezes. The droplets contain virus particles that can land in your mouth or nose and be inhaled into the lungs. This results in disease transmission.

Endemic. Endemic diseases are diseases that are always present in a given population at an expected/consistent level. An example of an endemic disease in the United States is chickenpox. Similar but different terms are “epidemic” (which refers to a disease that spreads more than expected in a given population) and “pandemic” (which refers to an epidemic that spreads across multiple continents or around the world).

Epidemic. An epidemic is an increase in the number of cases of a disease beyond what is expected in a given population. Similar but different terms are “endemic” (which refers to a disease that is always present in a population at an expected level) and “pandemic” (which refers to an epidemic that spreads across multiple continents or around the world).

Flatten the curve. Reducing the immediate spread of disease to prevent a spike in cases, which can overwhelm healthcare systems. To "flatten the curve" would distribute potential cases of the disease over a longer period of time, increasing the chances that enough resources will be available to treat them all. This is particularly important during the current coronavirus crisis. Of note, “flattening the curve” does not necessarily reduce the total number of people who will contract a disease. Instead, it changes the timeline.

Incubation period. The amount of time between being infected with a disease and showing symptoms. Also known as the latency period, this is when a person may be infectious to others without knowing it. The incubation period for COVID-19 is between 2-14 days (CDC, 2021a).

Influenza. Also known as “the flu,” influenza is a respiratory illness caused by one of several influenza viruses (influenza A and influenza B). Symptoms of the flu include fever, cough, fatigue, and body aches. The flu can cause complications and can be fatal for people who are elderly or immunocompromised. Flu viruses mutate over time, and new forms of the flu have caused outbreaks and pandemics throughout history, including the 1918 Spanish flu, the 1968 Hong Kong flu, and the 1976 swine flu. Some flu symptoms are similar to COVID-19 symptoms.

Isolation. Isolation is a public health technique used to help prevent the spread of disease. People who are diagnosed with a disease are separated from the general population so they can’t infect other people. Isolation is different from quarantine, which is the separation of healthy people who have been exposed to (but do not yet have) a disease.

Lockdown. "Lockdown," "shelter-in-place," and "stay-at-home" are different types of orders that many governments put in place to reduce the spread of COVID-19. These orders vary by location but often include limiting nonessential travel, closing schools, closing public spaces (such as bars, restaurants, nightclubs, and gyms), and encouraging or mandating people to stay at home except in certain circumstances. Unlike "isolation" (which is intended for infected people) and "quarantine" (which is intended for exposed people), lockdown orders are more widespread and are intended to be followed by everybody.

Middle East respiratory syndrome (MERS). This is a respiratory disease caused by a type of coronavirus that was first reported in Saudi Arabia in 2012. Its symptoms include fever, cough, and shortness of breath. According to the CDC, it is fatal in 30% to 40% of cases. Only two people tested positive for MERS in the US, both in 2014 (CDC, 2021b).

Mitigation. To reduce the impact of something. When COVID-19 could not be contained, countries entered the mitigation phase, hoping to slow its spread so health systems aren't overwhelmed with too many cases at one time. 

National emergency. The COVID-19 pandemic was declared a national emergency on March 14, 2020. This declaration unlocked federal disaster relief funding to be distributed to state and local governments to combat the virus.

Novel coronavirus. "Novel" is another word for "new." COVID-19 is referred to as being caused by a novel coronavirus because the specific virus had not been seen in humans before the current pandemic.

Outbreak. An outbreak is a sudden occurrence of a disease in a specific population.

Pandemic. A pandemic refers to the situation in which an infectious disease spreads across multiple continents or across the world. Notable pandemics include COVID-19, certain strains of the flu, cholera, and HIV. Similar but different terms are “endemic” (which refers to a disease that is always present in a population at an expected level) and “epidemic” (which refers to a disease that spreads more than expected in a given population).

Person-to-person. Transmission of disease from one human to another. The first case of person-to-person transmission of the COVID-19 virus in the US is believed to be between a woman who traveled to China and her husband upon returning (NYPost, 2020).

Quarantine. Quarantine is a public health technique used to help prevent the spread of disease. People who have been exposed to a disease are separated from the general population to see if they eventually develop the disease. Quarantine is different from isolation, which is the separation of people who have actually been diagnosed with a disease.

Serologic test. See "Antibodies."

Severe acute respiratory syndrome (SARS). This is a respiratory disease caused by a type of coronavirus that was first reported in China in 2002. Like COVID-19, SARS could cause severe respiratory problems and death. It was quickly contained. No cases of transmission have been reported since 2004.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This is the name of the virus that causes COVID-19. SARS-CoV-2 is in the family of viruses called coronaviruses. It is related to other viruses, such as the ones that cause SARS, MERS, and the common cold.

Self-quarantine. "Self-quarantine" is similar to "quarantine," but it is not mandated. People who think they have been exposed to a contagious disease are advised to voluntarily separate themselves from others and limit their movement and see if they become sick. Individuals who have been exposed to COVID-19 are encouraged to self-quarantine for ten days.

Shelter-in-place. See "Lockdown."

Social distancing. To maintain a distance (usually six feet) between yourself and other people. Unlike isolation and quarantine, social distancing does not necessarily require you to stay in one place.

Stay-at-home. See "Lockdown."

Symptomatic. Showing symptoms of a disease or condition.

Wuhan. The capital city of the central Hubei province in China, where COVID-19 was first reported. On Dec. 31, 2019, China alerted the World Health Organization (WHO) to a number of unusual cases of pneumonia in Wuhan. Several were traced to workers at the Huanan Seafood Wholesale Market (Zhu, 2020).

Vaccine. Vaccines are treatments that help the body develop immunity against infectious agents, like viruses and bacteria. After receiving a vaccine for a specific infectious agent, the body produces antibodies. Then, if the body encounters the infectious agent in the future, the antibodies help fight it. There are multiple vaccines that are widely available to prevent the spread of COVID-19. Getting vaccinated will protect both you and the people around you, and is essential for quelling the virus.

Zoonotic. An infectious disease that originated in animals and spread to humans. SARS-CoV-2, the virus that causes COVID-19, is believed to have originated in animals and spread to humans.


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

How we reviewed this article

Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

September 15, 2021

Written by

Health Guide Team

Fact checked by

Mike Bohl, MD, MPH, ALM

About the medical reviewer

Dr. Mike is a licensed physician and a former Director, Medical Content & Education at Ro.