Summary
Social norms are the informal rules of a group or society: shared, mostly unwritten expectations about how people should behave. ‘Mores’ is an older term for the norms a group treats as morally binding. Sociologists since Émile Durkheim have studied what norms do for social order.
More recent work asks what holds a norm in place. The philosopher Cristina Bicchieri argues that people follow one when they believe others do, and that others expect them to. The Stanford Encyclopedia entry she co-wrote reports the view that norms are “a kind of grammar of social interactions”: they say what’s acceptable, yet nobody designed them.
Rationale
Part 2 describes enculturation as how “people learn their norms and worldviews”. Of that pair, norms lie nearer the surface, rules we could state if asked; deep dispositions sit beneath and are harder to name.