A spot CLASS — street, action and board texture — where you measurably give up EV compared with how you play everything else. Judged against your own capture over the rest of your game, not against a baseline frequency.
The unit is the class, not the hand and not the statistic, because a class is the only thing you can be dealt again. "You lose 4.2bb per river call on flush-completing boards" names a spot a drill can reproduce and a later re-measurement can check; "your WTSD is 3% below baseline" names nothing you can practise. A class has to clear a minimum sample and separate from the rest of your game by more than its own noise before it is called a leak at all — and until it does, it is shown as a hint. Nothing about how OFTEN you act makes something a leak here; that is frequency context, which is a different entry and never a verdict.