Comedy is a drama term that refers to any story with a happy outcome, which usually includes humor. Comedy movies are supposed to be humorous as well. Sitcom, however is a word that stands for the phrase "situation comedy," which is usually a TV show that depicts potentially real situations or circumstances with humorous outcomes. Shows such as Frasier, Seinfeld, Parks and Recreation are all examples of sitcoms.

Agree with the previous answers. To further explain sitcom (situation comedy), it's usually a TV series with many episodes. The story is usually based in the same location, for example the same house, or the same bar, or the same office, etc. A comedy is generally any type of performance (television, movie, theatre) that is intended to make the audience laugh. So a sitcom is a particular type of comedy.