A stereotypical is a generally held, simplistic, sometimes essentialist view of a certain group. Sex, gender identity, race and religion, country, generation, economic factors, culture, and other factors are frequently used to stereotype populations. Stereotypes are firmly ingrained in social structures and culture as a whole.
There are also several social stereotypes regarding social groupings, ranging from "girls stink at arithmetic" and "guys are so nasty" to "he's growing a little senile with aging" as well as "black people suffer at universities." Almost all of these instances are likely to be familiar to you. In essence, stereotypes are similar to air in that they are both undetectable and always there.
We all enjoy proving a point with smart-sounding generalizations, generally accompanied by a statement like "I just read an article about..." or "No way, truly, this is completely accurate." Preconceptions, on the other hand, easily crumble in the face of unflinching data. And, as with many things we take at face value, many of these prejudices turn out to be nonsense.