Definition:
Stereotypes are ideas we have from countries, nationalities, people, etc. that are widely shared by people, due to the spreading of them. When something is a stereotype, we call it stereotypical.
Etymology:
The word comes from the French adjective stéréotype. "Stereo-" means "fixed" or "unchangable" and "-type" means "impression" (in this case do not refer to a physical impression, rather a mental impression) and also typical. So, "fixed/unchangable" + "impression" = a fixed and typical impression of a specific person or group of people.
Hope it helped,
BioTeacher101