A T1 lift is the primary exercise movement, like a squat, bench press, deadlift, or overhead press. It is the priority of that training session. A T2 lift is a variation of the T1 lift (e.g. a front squat is a variation of the back squat, a deficit deadlift is a variation of a deadlift, etc.). A T3 lift is an accessory for muscular development and is done in higher rep ranges than T1 or T2 lifts.