Well in my opinion it depends on wether we mean "for the purposes of Civ" or "In general" In general I think there are few civs/culture groups. Civs are things like Greco-Roman, European (Post fall of the Empire or maybe Charlemagne, includes Latin America and the Anglosphere), Sub-Saharan African, North African (Though often Nth Afr is inhabited by people of Greco-Roman, European, or Arab culture), Arabic, Indian/South Asia, East Asian, Slavic(?), possibly South east Asia, Fertile crescent civilization (Usually those peoples inhabiting the ME before the Arabs), and Meso-American. Basically this broadly encompasses city building culture groups. Now clearly this would not do for a Civilization game, for civs purposes I usually define a civ as a Nation (belonging to one of the aforementioned civilization) with power and influence over a wide area for it's time and place. However in some cases I'm willing to see a single culture represented as a civ (i.e. I would rather Scandinavia to Norway/Denmark and/or Sweden, and I'm willing to allow Germany to stand in for Prussia and the HRE) also though, Rule of Fun applies.