Real Dictionary

tribe
Tribe is sometimes used to refer to a group of people of the same race, language, and customs, especially in a developing country. Some people disapprove of this use.
You can use tribe to refer to a group of people who are all doing the same thing or who all behave in the same way.

tribe in American English
esp. among preliterate peoples, a group of persons, families, or clans believed to be descended from a common ancestor and forming a close community under a leader, or chief
noun: any aggregate of people united by ties of descent from a common ancestor, community of customs and traditions, adherence to the same leaders, etc

tribe in British English
noun: a social division of a people, esp of a preliterate people, defined in terms of common descent, territory, culture, etc