Chaos Undivided
Chaos Undivided is a belief among followers of Chaos in Warhammer 40,000. Formed by Lorgar, the Primarch of the Word Bearers, Chaos Undivided holds that the Chaos Gods are a pantheon of Gods, or venerate Chaos as a unified whole. Followers of Chaos Undivided maintain that worshiping all four Gods allows one to draw on all the strengths of the Chaos Gods without falling to weaknesses (Khorne's all out rage, Slaanesh's need for sensation, Nurgle's decaying influence, or Tzeentch's more detrimental mutations).
While followers of a single god (such as the World Eaters, the Thousand Sons, or the Emperor's Children) would hold that they are weaklings who cannot chose a single God to venerate, there is some evidence to its benefits. Of the Traitor Legions who follow Chaos Undivided (the Black Legion, the Iron Warriors, and the Word Bearers), these three have not fractured into disunited warbands, and are actually able to maintain the drilled discipline one would find in the Adeptus Astartes, allowing them more precision than a follower of Khorne or Slaanesh would show. Oh, don't get us wrong, companies and hosts will still go to war with each other at the drop of a hat, but it doesn't take their Primarch telling them to stop dicking around to get them to stop, like the World Eaters and Emperor's Children. On the other hand, the greatest Champion of Chaos Undivided is Ezekyle Abaddon, the Warmaster of Chaos.
The most well-known to /tg/ follower of Chaos Undivided would be the fangtoothed woman who calls herself 'Cultist', with a close second being her long suffering guardian.
Chaos Undivided used to be thought of as a force of its own, not dependant on the Gods, but Aaron Dembski-Balden has said that that isn't canon any more.