This describes a particular type of price action where price swings up and down absorbing supply and demand levels as it goes. It's important to understand what exactly is happening here so that when this price action develops we know how we can react to it.
Compression into Supply
As price rises creating higher highs and higher lows, each time it swings back down after a rally its absorbs demand. There is a reason why price does this.
These demand zones are standing the way of a nice big short so the buy orders at these levels need to be absorbed before price can fall freely through this area. Pro money moves price in this fashion to clear the path for a short whilst using the buy orders to build their short positions. When you see this happen below a supply level, once the last demand level is absorbed and the supply level is reached, price will often fall quite easily down through the area. This area or this type of price action is known as compression.
Compression into Demand
The same price action can be seen going into demand zones where price absorbs supply whilst moving down. Pro money clears supply on the down move to make way for a long whilst using the sell orders to fill their long positions. Once the last supply level has been absorbed, price will often rally quite easily through the compressed area.
Identifying this PA will give you a clue as to where price will turn and how far it will move.