Political correctness is the practice of being careful not to offend or exclude anyone, especially people who belong to groups that are frequently discriminated against. Comedians who don't worry about political correctness sometimes get themselves in trouble.
In the 1970s, political correctness was seen as a way to avoid hurting people's feelings or deeply insulting them, but the phrase soon took on an ironic or critical slant. Today, most people who use the term mean it as a criticism of being overly careful: "Saying 'fire fighter' instead of 'fireman' seems like political correctness that's gone too far to me." Conservatives in particular see political correctness as a liberal worldview imposed on every aspect of culture.