Among White Wolf's online community, the term splat has come to mean a particular genre or ruleset for play in the World of Darkness game setting.

Though each of these "splats" have the same core rules, each different "super" (as they are also known) has certain powers and abilities. For example, in M:tA, one gets to cast magic. But in V:tM, you get disciplines and other vampiric powers.

Here is a listing of the official splats:

Information gathered from:
White Wolf Game Studio's old website (http://www.white-wolf.com/home2.html)
My own mind & memory