What’s a custom when it comes to social studies

A custom is defined as a cultural idea that describes a regular, patterned behavior that is considered characteristic of life in a social system. Shaking hands, bowing, and kissing—all customs—are methods of greeting people. The method most commonly used in a given society helps distinguish one culture from another.

Explanation:

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.