If you reach the point where you cannot perform another rep, you’ve trained to failure. If you reach a point where you can’t perform another clean rep, you’ve reached technical failure. This can happen in any rep range. I think you have the misconception that “training to failure” would have to be done with an extremely light weight for a seemingly infinite amount of reps. “Lifting heavy” isn’t really a style of lifting or even a real term. It’s just lifting heavy ass weights, doesn’t mean that it’s a certain number of reps. You could “lift heavy” and “train to failure” at the same time…crazy stuff huh?