A role is the
behavior and anticipated
reactions expected from someone who occupies a
status position. It's sort of the
protocol associated with a
status position and usually entails
participation from more than one person to really manifest itself.
Examples of this are really common. You expect certain characteristics of people who surround you. We expect teachers to maintain a persona of objective supportiveness and when they violate those expectations we are startled. When a teacher has a temper tantrum or accidentally uses profanity in the classroom they have stepped outside of the role of teacher and into something like pissed off person.
Obviously most people assume several roles over the course of a day: father, mother, worker, co-worker, and on and on. Sometimes this leads to role conflict and other troubles keeping things straight.