A "stereotype" is a common idea about a group of people. For example, people have stereotypes about different nationalities:
- Americans are loud.
- Russians drink a lot of Vodka
...and so on.
People also have stereotypes about certain professions (like police officers and lawyers), different regions (Northereners, Southerners, etc.), races, age groups, and so on.
When a person follows the stereotypes about a group that they belong to, you can say that they are "stereotypical":
He's a stereotypical teenager: moody, immature, self-absorbed.
You can also use the phraes "your stereotypical ___":
A: What's she like?
B: She's your stereotypical fitness instructor.
This means "she fits the common stereotypes about fitness instructors".
Stereotypes are usually negative, and it's usually not a good thing to admit that you have stereotypes about a group of people.