A fixed idea or image that many people have of a particular type of person or thing, but which is often not true in reality -- is a Stereotype.
We cannot really say if most are true, but some are true, and not all are true.
“Labels are for filing. Labels are for clothing. Labels are not for people.” -- Martina Navratilova
Stereotyping (races) is saying that--
all Blacks are good at sports or
all White in general reflect those of upper class.
Stereotyping (gender) is saying that--
Guys are messy and unclean or
Woman have the sole responsibility to clean up the mess or
Girls are not good at sports or
Men who spend too much time on the computer or read are geeks.
Stereotyping (culture) is saying that--
All Arabs and Muslims are terrorists or
Italian or French people are the best lovers.
If you think in terms of labels then you will hardly escape labeling yourself too and once you start thinking that way you will lose your self confidence in no time.
The problem with stereotypes isn't only their content. It's the stereotyping.
You can be the perpetrator or the victim of it.
If you find yourself stereotyping someone (and we all do it. I do it. All the time. So do you.), take a step back and ask yourself. Why do you believe this? Why are you generalising this?