A stereotype is a belief about a group of people that is not necessarily true. It is a generalization that assumes that all people act the same way. Some examples of stereotypes are: African American people are all good at basketball. All Asian people are good at math. People with blonde hair are stupid. And so on.
To perpetuate something means that a person causes or allows something to continue.
Therefore, perpetuating stereotypes would mean using or believing a generalized (and often untrue) belief about a group of people and spreading that belief.