Overgeneralized beliefs about a group of people that often underline prejudicial emotions are called

Overgeneralized beliefs about a group of people that often underline prejudicial emotions are called "stereotypes".

A stereotype refers to a settled, over summed up conviction about a specific gathering or class of individuals.
One advantage of a stereotype is that it empowers us to react quickly to circumstances since we may have had a comparative ordeal previously. One disadvantage is that it influences us to overlook contrasts between people; consequently we ponder individuals that won't not be valid.