A role is a part you play. In school, you might take on the role of clown, in your family, the role of the responsible one, on stage, the role of Juliet.
Role can also mean job or function. It is the role of the police to keep the community safe, and political parties often argue about the role government should play in our lives. Roles can also be played by things. You can say that computers play an increasing role in our day-to-day lives and that the role of a hat is to keep your head warm. You look up to your role model because of the important role that they play in influencing others' lives.