A bigot is someone who doesn't tolerate people of different races or religions. If you have an uncle who is a bigot and tells racist jokes at Thanksgiving, you may need to talk to him and tell him it's not okay.
A bigot can also be someone who refuses to accept other ideas, as in politics. This word was borrowed from Middle French, but the French word is of uncertain origin. In Old French bigot was a term of abuse for Normans, and possibly related to the oath bi got "by God." In English and French, a bigot was originally a hypocrite, a person who claims to have certain moral beliefs but whose behavior doesn't match those beliefs. A bigot was specifically a hypocritical professor of religion, but the connection with the current sense of bigot is not clear.