A role model is someone others look to as a good example. A role model is someone who is worthy of imitation — like your beloved teacher or a well-behaved celebrity.
Just as a model is something that represents an inspirational ideal, a role model is someone who inspires others to imitate his or her good behavior. Parents try to be role models for their children by being good people. A famous person who gives money to charity or helps sick children is a role model. If someone behaves badly, you could say they're a negative or bad role model — the kind of person who shouldn't be imitated.