Crumpling

Crumpling is a term used in the Street Fighter series and other fighting games to refer to a slowly falling opponent.

Description
Crumpling is signified by the character slowly falling, generally on their knees, before lying flat on the ground.

Street Fighter IV series
Prior to the Street Fighter IV series, opponents would only crumple when knocked out by chip damage. The series introduced another method of crumpling: the Focus Attack.

If a regular Focus Attack hits an opponent mid-attack, the counter hit will crumple them, leaving them open to attack. Level 2 and Level 3 Focus attacks have an inherent crumpling ability, in return for longer charge time.

Focus Attack crumples are a popular way to combo into an Ultra Combo.

Street Fighter X Tekken
Similar to the above, Dash Cancelling a Level 2 Super Charge turns the next hit into a counter hit that crumples the foe.