Jungling
Jungling is a term borrowed from League of Legends and refers to the neutral ground which is not a part of the main lanes players start the game in. This area is characterized by the presence of Denizens aka Jungle Creeps. The purpose of these "camps" is to provide a source of souls that don't come from troopers or killing enemy players.
Strategy
The purpose of the jungle is to allow players to gain souls while not being in their lanes or fighting other players. While the intricacies of the game are complicated concerning who should jungle, how often and when, the common consensus is that "Carries" are characters who become borderline unstoppable given enough souls and are often given priority in team composition when jungling.
Typical examples of this are Infernus and Seven.
Other characters will have lower priority for jungling as a result of getting souls from other sources, such as Vindicta's access to Assassinate granting her bonus souls on kill or support characters such as Kelvin or Dynamo not needing power spikes to keep their teams healthy.