1. offensive slang A shortening of "retard," a derogatory term for a person who has an intellectual disability (formerly called mental retardation). A: "Sarah's brother is a tard, so she always has to stay home to take care of him." B: "Why do you always have to say awful things?"

2. offensive slang By extension, a derogatory term for someone who is stupid, foolish, or socially inappropriate. Stop being such a tard, Tom, and do this the right way.