What is the difference between pandemic and epidemic ? Do infectious and contagious mean the same thing ? How exactly does contact tracing work ? Even native English speakers may not fully know the answers to these questions . As English learners , you have probably noticed some words and phrases you do not understand when reading reports about the new coronavirus . Today , we look at some of the most common COVID-19 terms . We can start with epidemic versus pandemic . An “epidemic ” is when a disease spreads through a population and affects many individuals at the same time . An epidemic may affect a community , province or even a whole country . A “pandemic ” is a kind of epidemic -- one that spreads to a much larger area or even worldwide . Like many medical-related terms in English , the word comes from Greek . Pan - means “all or every .” The second part of the word , “-demic ,” comes from the Greek word demos , meaning “people .” On March 11 , the World Health Organization (WHO ) declared the coronavirus crisis a “pandemic .” At a news conference that day , the WHO's director-general said , “Pandemic is not a word to use lightly or carelessly .” He was reminding people that the word is used only for the most extreme and dangerous situations . The virus is now present in 213 countries and territories worldwide . Infectious -- the adjective form of infection -- describes diseases that are spread through the environment . Malaria , for example , is an infectious disease . Humans contract the disease through mosquito bites . Malaria , however , is not contagious -- or able to be passed from one person to another . You already know that COVID-19 is easily passed person to person . Common colds and the seasonal flu are also contagious and infectious diseases . The new coronavirus has spread quickly partly because those infected can be contagious before they even know they are sick . In other words , those people are asymptomatic . This word has a lot going on . Let's break it down . A “symptom ” is a change in the body that shows a disease is present . For example , we wrote on March 30 : “Most people who get COVID-19 experience mild or moderate symptoms , like coughing and high body temperature , or fever .” “Symptomatic ” is the adjective form of symptom . It means “showing that a disease is present .” So , we could say : “A cough and fever are symptomatic of the new coronavirus .” The prefix “a -” means “without .” So , what happens when we add the letter “a ” to “symptomatic ?” The word ends up meaning “having or showing no signs of disease .” Experts know that asymptomatic people can spread the disease . This is partly why officials are urging people to stay at home as much as possible . In some cases , whole countries were put in lockdown -- a state of restricted movement put in place as a security measure . Most people around the world are social distancing . This term is new to everyday English . The World Health Organization is now using the term “physical distancing ” instead of social distancing . The term is a little more exact because people can socialize without being near one another . Social distancing is less extreme than quarantine and isolation . Isolation separates sick people who have a contagious disease from people who are not sick . Quarantine restricts the movement of people who were around a contagious person to see if they get sick . In the case of COVID-19 , the recommended quarantine period is two weeks , or 14 days . The word was first used in the 1400s in Europe and meant “a period of about 40 days .” Quarantine can be a noun and a verb . Many experts say in order for it to be safe for places to reopen , widespread testing and contact tracing need to be in place . Contact tracing requires investigative action . Tracers work with confirmed COVID-19 patients to learn whom they have been close to . The tracers then inform those people that they may have been infected . The tracers also provide advice on what actions to take . In some places , such as South Korea and Singapore , contact tracing started early in the pandemic . Social distancing , isolation and quarantining are all done to help “flatten the curve .” This phrase , now extremely common in the age of COVID-19 , means to slow the spread of disease . The same number of people might get sick , but infections happen over a longer period . This eases the pressure on emergency and health care resources . Hospitals in most areas have a limited number of beds and breathing machines , called ventilators . These machines are extremely important for treating patients with more severe cases of COVID-19 . The health care industry is also limited in respirators . These are special masks , or nose and mouth covers . Medical workers need respirators to protect themselves from contagious patients . Chambers also used the term “physical distancing .” This is not as commonly used as social distancing . The two phrases mean the same thing .