stereotypes are a way to "put a label on someone" so therefore is a form of prejudice if you do not know the person
but only if you do not know the person or haven't met them.
putting a label on someone you know is not prejudice
prejudice is pre judging an individual before meeting them
so there are ways that stereotypes can differ from prejudice because if you know the person, placing a label on them would not be prejudice.