Assuming you mean to understand the word stereotype used in sociology, let me quote from FumbleFingers:
stereotype - is a preconceived and oversimplified idea of the
characteristics which typify a person, situation, etc.; an attitude
based on such a preconception. Also, a person who appears to conform
closely to the idea of a type.
I prefer not to be known by my friends to be using stereotypes rather than studying and analyzing the facts closely. It is when one classifies a group of people or things, and this can make the picture one has of that group quite inaccurate.
It can be used as a noun or a verb. Example for stereotype as a verb: "to form a fixed and often untrue or only partly true idea about". You can also 'stereotype' a group of people 'with' an assumption.
It's unfair to stereotype people according to where they live.
It's not fair to stereotype a whole group of people based on one
person you don't like.
Movies have stereotyped the hooker with a heart of gold ad nauseam.
Example as a noun and this is quoting from Dictionary.com:
The black community cannot pretend that the stereotype of black men as
violent comes out of nowhere.
Sometimes looking at the adjective or derivatives would help understand and use the a term correctly.
Quoting from Urban Dictionary about Stereotypical:
A stereotypical person is one who is the image of a stereotype. It is
NOT (I repeat, NOT!!!!) a person who believes that stereotypes are
true. Only a stereotypical foreigner would think this, because the
stereotype of foreigners is that they are bad at English.