The crush system in Tekken 7, allows certain moves to make the character not get hit by high or low attacks, called high crush and low crush respectively. It works by the move causing the character to enter crouch or jump after a number of frames from the startup of the move.
High crushing moves will evade highs by causing the character to crouch during the move. This is might be referred to in frame data as tc (technically crouching) or cs (crouching state).
The generic d4 is an example of a high crushing move. It connects on the 12th frame after startup, however will make the character enter a crouching state on the 4th frame.
An in-game example of this would be Claudio 2,1 on block (-6) into d4 (cs4) would beat all highs including the generic standing jab.
Low crushing moves will evade lows by causing the character to jump during the move. This is might be referred to in frame data as tj (technically jumping) or js (jumping state).