Pre-exhaustion in training/bodybuilding terms tends to be used as a cover all definition for anytime an exercise, usually a one joint isolation move, precedes a compound exercise. For your program pre-exhaustion is going to fall into three more specific categories:
PE = pre-exhaustion. This can be because we want to fatigue the certain prime mover muscles so that the stabilizers (think the lower back, core, shoulder girdle for squats) don’t have to work as hard. Especially if the afore mentioned muscles are a weak link in your particular kinetic chain or compromised because of injury history. For example, 5 x 10 leg extensions or 2 x 30/30 1-leg leg-press before squats. Another example would be chest flyes before pressing to bring lagging pecs up to speed. If your exercise prescribed has “PE” before it think get a burn!
PW = Pre-work, exercises in this category are primarily for blood flow. I particularly find value in pumping the antagonist/stabilizer muscles with blood before a compound lift. For example, leg curls before squats. We aren’t necessarily try to destroy the hamstrings but surge blood to the knees and turn on the hamstrings before performing their stabilizer and secondary roll. Linked here is a T-Nation article discussing the topic of Leg Curl First, Squat Later. Something that I’ve found useful for trainees with shoulder issues, especially anterior humeral glide, is high-rep rows or iso-metric batwing holds before pressing. Also, this could be prescribed to help pump blood flow to joints especially if you have issues such as elbow tendinitis.
MM = Mind Muscle connection. If this preface is used before the exercises the main purpose is help the mind muscle connection. For example you might have hip-adduction machine reps before before squats if your adductors aren’t firing during the squat which can often lead to over emphasis on the lumbar spine. Another example would be 1-arm bench press before your barbell bench, or lat raises before overhead press. These exercises should be done generally with RPE7 intensity.