In common usage, "culture" means "the customary beliefs, social forms, and material traits of a ... social group" (m-w.com). In Europa Universalis II, culture is simpler: it's basically just a number. In EU2, there are lots of cultures, but two cultures are either the same, or they are different. There is no such thing as "similar". Three entities in EU2 have culture: countries, provinces, and settlements.