Split Team is a tactic often using in Guild versus Guild matches. When doing a split, the guild operates with 2 separate teams (usually consisting of 4 players each, however other splits are possible), instead of fighting 8 vs 8 as usual.
The advantage of splitting lies in either forcing the opponent, who might not have a team that is good at splitting, to split as well, or to control either the Flag stand OR the enemy guild hall (where the split team will kill NPCs and/or eventually the Guild Lord) while the other team has to run back and forth between the two. Good split teams manage to outmaneuver the opponent, managing to fight many small and quick battles with overwhelming odds. Disadvantages include the increased coordination needed, the possibility of loosing the flag stand for a prolonged period of time and the possibility of one part of the split being killed of by the full enemy team.
Some Guild Halls are more in favor of splitting tactics, while others make it hard to split (notably the Burning Isle).