From the White Wolf Wiki, the most complete White Wolf reference

A troupe is a group of players participating in a roleplaying game, especially in troupe games, in which each player may take on the roles of multiple characters.

The troupe style of gaming can be played with any game, but games which are troupe games by default include:

• Ars Magica - each player portrays a mage, one or more of their companions, and any number of grogs - minor members of the main character's retinue. While companions are often unique to each player, grogs are commonly shared between members of the troupe.
• Wraith: The Oblivion - each player is also the "Shadowguide" for another player, portraying the other character's Shadow, the dark side of their personality.