Heavy lifting has a lot of different definitions.
I would personally describe lifting heavy as using a weight that you can only do for 2–5 reps. (For a single rep it’s a different category - a ‘one-rep max’.) If you’re using a weight which takes a ton of effort for you to move, and at most you could do 5 or 6 reps with it, then that’s lifting heavy.
What, no number value? No ‘if you’re using triple digits it’s not heavy’?
Of course not.
Everyone is different, and that’s the beauty of weightlifting. If I go into the gym and deadlift my max - it’s been a while but that used to be 180kg. At the same time, the biggest guy in the gym is doing his max, something like 240kg. AND at the same time, my more casual training friend is doing his max, 80kg. Then who’s lifting heavy? We all are.
If we’re all pushing our limits and giving it everything we’ve got, that’s lifting heavy. It’s a personal definition.
Don’t believe me? Think of it the other way around?
Talk to that biggest guy in the gym when he’s warming up with 160kg. To him, that’s pretty light - it’s a warmup. That would mean his max of 240kg is truly lifting heavy compared to everyone else, right?
My current training partner who has been powerlifting competitively for years is far stronger than myself. We will be going through warm-up sets, preparing for our working set(s) and 2 sets in he will already be on MY working weight of 180kg.
All of a sudden, my mate is only lifting lightweight. It doesn’t make sense.
Heavy lifting is whatever is heavy for you. I’d define it as the point of only being able to do 2–5 reps. The weight doesn’t matter - if you nail those 5 reps, you’re practically the same as a stronger person doing their 5 maxes. And next time you do, know that I’m sending a high-5 your way.