A group of people who share common characteristics, such as language, physical appearance, customs and traditions , is called a(n)

Ethnic Group

Explanation:

Ethnic group - a community or population made up of people who share a common cultural background or descent.

Ethnic Group

Explanation:

Group of people who share common ancestry, language, religion, customs, or a combination of such charactertics.

an informal structure in a bureaucracy would be something like so-called "office politics". where there's a formal structure set up for the organization, but then an informal subculture as well that has a way of organizing the bureaucracy further. this can be positive because it sets up an added degree of organization, albeit informal, within the bureaucracy.