TrueSkill™ (TS) is Microsoft's skill-based ranking system that comes with GFWL for Dawn of War II and Dawn of War II: Chaos Rising online multiplayer. The purpose of TrueSkill is to estimate the actual skill of the player, while Rank is just about the amount of games they have played.
The TS scale theoretically goes from 1 to 50. To outline it roughly, in Dawn of War II players with a TS rating under 20 used to be considered low skill, 25 or more was good, 30 or more was excellent and 35 or more was elite. Over 40 happened very rarely. Since much of the player base moved to Dawn of War II: Retribution after March 2011, attaining a high TS rating became significantly easier.
With the release of Dawn of War II: Retribution, the TrueSkill system and GFWL matchmaking were abandoned in favor of Steamworks matchmaking and a modified Elo rating system.