Short answers, pulled from the story.
The word clan comes from the Gaelic word clann, meaning "children," "offspring," "progeny," or "descendants." According to the Oxford English Dictionary, it entered the English language around 1406 as a label for the social organization of the Scottish Highlands.
A totem is a non-human figure, frequently an animal, that serves as the symbolic founding ancestor of a clan. Traditional anthropological thought, as represented in the work of Gerardus van der Leeuw, classified these non-human clan ancestors as totems.
Clan exogamy rules prohibit marriage between members of the same clan, treating shared clan membership as sufficient grounds to exclude a match as incestuous. Some societies extend the ban to include the clans of both parents or even all four grandparents.
Scottish clans are unique in their use of elaborate tartans, insignias, and mottos as markers of identity, a system not found in most other clan traditions. Their culture also includes clan gatherings and the Highland Games, and was shaped by the Highland Clearances and the Jacobite uprisings.
An Irish clan, called a fine in Irish Gaelic, included the chief, his patrilineal relatives, and unrelated clients of the chief who had taken on the clan's name to show allegiance. Only patrilineal relatives were eligible to be elected chief; clients and their descendants were excluded from that role.
The term varies by country and kingdom: ubwoko in Rwanda, umuryango in Burundi, ruganda in the Bunyoro and Buhaya kingdoms, igise in Buha, ishanja in Buhavu, and ebika in Buganda. Rwanda has twenty clans, each divided into subclans, while Nkore has only four clans.