Cabals in The Secret World are the same thing as guilds in other MMORPGs. Very little information has been released regarding cabals except that they will play a vital role in PVP. Players are not required to join cabals in order to play the game, but will have more content open to them if they do join one.
Cabals are easy to create in the Secret World. Basically at a certain level anyone can make a Cabal there is no cash value nor requirements for x number of members to create the cabal..
Another benefit to being part of a cabal is that there will be cabal housing in the game. Little information has been released on housing, however, it has been confirmed that the housing will reside outside the faction headquarters.
Cabals will be able to furnish and decorate their housing. Also there will be streamlined leaderboards tracking the success of cabals. These leaderboards not only measure in PVP, but also other aspects such as exploration, crafting, and PVE missions.
The leaderboards will grant rewards to those holding the number one spot such as special titles for cablas or players. They will be available both inside and outside of the game.