Which term specifically describes the categorization of people into ethnic groups without taking into account individual differences?

I'm pretty sure that's just Ethnicity?

It categorized into "Ethnicity".

Explanation:

Ethnicity is the social identification that indicate particular group which is often descended from common ancestors.

These member of the group share common cultural traits such as beliefs, values, habits, language, dress, religion, norms and customs.

Sharing of common cultural tradition, ethnicity is the complex it involves more than just place of birth or color of skin.

for example ethnic groups like american, Russian, Jews all categorized in "WHITE" race ethnicity.