That label is entirely mine and entirely for my own mental processes.
I call the heavier sets that target the same major muscle group as the main work “supplemental,” so here:
- DB press “supplements” overhead press → shoulders
- BB row “supplements” deadlift → lower/upper back
- Weighted dip “supplements” bench → chest & tris
- BB hack squat “supplements” squat → lower body
I guess I do that because, as I understand it from Forever, I could choose pretty much the same collection of second movements for the supplemental work in many other 5/3/1 templates. I also run all of those sets immediately after the main work, and I try to keep them (way) under 20 minutes, just like I typically do in other 5/3/1 templates.
And I guess I call the rest “assistance” because it tends to be lighter DB or machine work and I run it in a circuit, just like I typically do in other 5/3/1 templates.
But really it matters absolutely not at all.