Physical distancing is the name given to a set of behaviours which maintain space between yourself and other people who live outside of your household.
COVID-19 is primarily transmitted between individuals through respiratory droplets when an infected person coughs, sneezes or talks and by contact with contaminated surfaces, objects, and hands. A person becomes infected when the COVID-19 virus enters the body through the mouth, nose or eyes.
The main mode of COVID-19 transmission is thought to be via respiratory droplets, but may also be via smaller airborne particles– either way keeping physically distanced is one of the main ways of reducing the spread of the virus. If people do not come into close contact with people outside their household, then the likelihood of inhaling or coming into contact with infectious respiratory droplets decreases. Physical distancing should always be done in combination with other preventative actions like handwashing with soap, surface cleaning and mask use.
This article from the Washington Post provides a nice visual overview of how COVID-19 transmits from one person to the next and how different measures of physical distancing can help reduce this transmission. The videos below also provide easy-to-understand metaphors for why keeping a distance can interrupt the spread of COVID-19.