Stereotypes are mentally constructed simplifications of groups of people, events, and things while compartmentalizing, which can either be positive or negative during overgeneralization.
All people from Africa are black. All black Africans are poor and barbaric. All Thai students cheat during exams. Professors don’t make mistakes, and their students are academically excellent. Many Thai people have the perception that all foreigners are rich.
Here we have two sets of stereotypes. Stereotypes can be negative, like the first three stereotypes; or it can be positive, like the last two stereotypes.
With these examples given, it might be easier to explain what stereotypes really are.
Because the world is too big, too dynamic, and too complex for us as human being to understand it in all its detail, we have an urge to classify and categorize everything into compartments or pigeonholes. It is easier to handle and accept smaller groups, and it makes sense. The problem does not lie with this compartmentalizing or pigeonholing, it lies with the fact that we tend to overgeneralize these compartments. These overgeneralizations are often negative evaluations of these members of these compartments. For example, we know that all Africans are not black, and that there are rich and civilized black people. We also know that professors do make mistakes and that of their students are average, and that most foreigners in Thailand are not rich.