From WikiFAQs

A Faction is an organized group of users on a board. There are two types of factions: Community and Political.

Community factions are essentially social boards with rosters, and the roster serves as a sort of measure of status. Goals for these factions do not go far beyond having fun and making the board better.

Political factions are organized with some sort of administration to fulfill an agenda. Normally there is a form of rank structure to it and a code of conduct that the faction upholds.

A list of most factions and other boards can be found on the Secret Board Directory found on Zamzara.