What is the difference between quarantine and isolation?

Disease vs exposure: Usually one is in quarantine when one actually has been diagnosed with an infectious disease (COVID19, flu, leprosy, etc) which could spread to others. One in quarantine stays completely separate from others for a defined period. Self isolation is usually for someone who has been exposed to such a disease but not definitely diagnosed with it, who stays apart from others while observing for Sxs

Quarantine/isolation: Isolation separates sick people with a contagious disease from people who are not sick. Quarantine - People who have been exposed to a contagious disease are separated from others while waiting to determine if they become ill. COVID has given us examples of requirements for each.