Liquidity is the ability to transact
A liquid area is one where orders can be matched with less disruption. On a chart, traders often infer possible order clusters around obvious highs, lows and widely observed levels.
A sweep is not a signal by itself
Moving beyond an obvious level may trigger resting orders, but it does not guarantee reversal. The response after the level is traded is more informative than the touch alone.
Map areas, not certainty
Liquidity concepts are best used to form questions: where may orders be resting, what reaction would matter, and what behaviour would invalidate the idea?