T-101 is an Infiltrator. In the NES game The Terminator, a T-101 is a Terminator. In T2: Infiltrator, a T-101 Infiltrator is T-90 Humanoid Hunter-Killer with living tissue outer sheath, utilized to infiltrate human group. In the Terminator 3: Rise of the Machines film, a T-101 Terminator is a Terminator with Model 101 outer sheath.
It can be seen during the final battle.