In Crusader Kings, a character's culture is the group of people whom the character is most closely related to. A province's culture is which group of people make up the majority of its inhabitants.
Religion[]
Cultures are associated with religions; for example the Norman culture is considered Catholic. Some cultures are not playable because they are associated with Islam or a pagan religion, unless the certain character has converted to either catholicism or orthodox.
How Culture is Determined[]
When a character is born, his or her culture is determined by either their father's culture, their mother's culture, or the culture of their country's capitol.
Effects of Culture[]
A character's culture determines what names they can have, as listed in db/character_names.csv