Progressive overload is the idea that your body only changes when you ask more of it than it's used to. That's the whole concept. The complicated-sounding name covers a simple practice: add a little weight, a rep, or a set over time, instead of repeating the same workout indefinitely.
The mistake most people make isn't misunderstanding the idea — it's not tracking enough to apply it. If you don't know what you lifted last week, you can't tell whether this week is actually harder. That's the entire reason a training log matters more than a workout plan on its own.
There's more than one way to add load. Weight on the bar is the obvious one, but reps, sets, tempo, and rest periods all count. A coach's job is choosing which lever to pull each week based on how you're recovering, not just running up the weight every session regardless of how you feel.
It's also not linear forever. Most lifters hit a point where adding five pounds a week stops working. That's where periodization comes in — planned lighter weeks, rep range changes, and exercise variation that let you keep progressing without grinding yourself into the ground.