Institutions

An institution, in this sense, can be defined as a "pattern of shared, stable, behaviour". In other words, it represents the idea that people's behaviour is organised (patterned) in ways that help to maintain the stability of the social system.

Thus, "family life", for example, is an institution because it represents a basic pattern of behaviour to which the majority of people in society conform (and which has existed, in some shape or other, for many generations).