Out-group homogeneity bias
Out-group homogeneity bias is seeing members of other groups as all alike while seeing members of your own group as varied individuals.
In everyday life
An older adult says 'teenagers all act the same', while describing each of their own friends as very different from one another.
You describe the people at a rival company as 'corporate robots who all think the same way', while you describe your own coworkers as a colorful mix of personalities.
Why your mind does this
Trusting people and things we know is usually safe, because familiarity means we have dealt with them before without harm. Favoring our own group helped our ancestors cooperate with the people they depended on. Liking what is close and known also saves the effort of judging everything from scratch.
Its family, in 30 seconds: Familiar is better
How to spot it
Notice when you describe another group with 'they're all' and your own group with 'we're all different'.
How to counter it
Try to name three ways members of the other group differ from each other.