Fall Damage Cancel is a glitch in Dark Souls which allows you to negate any fall damage (even lethal) until a certain height without the need of a Fall Control Quitout. The glitch can be performed with and without Fall Control, the Fall Control version being easier as no timing is required.
To perform the glitch without Fall Control, the player needs first to fall off a ledge, then mid-fall plunge attack another ledge so that the character enters the landing animation of the plunge attack but slides off the ledge at the same time. This results in the character falling down to the ground while still being in the landing animation of the plunge. This allows the player to roll mid-air just before the character hits the ground, negating all fall damage due to the invincibility frames of the roll.

Notes:
It is possible to roll later in the plunge animation by rolling and starting to hold direction on the same frame. Normally it is done using keyboard rebinds as it is frame perfect otherwise.
Example rebinds:
To perform the delayed roll the player needs to first press L.Shift then press Z and release L.Shift within 4 frames of pressing it but after pressing Z.
To perform the glitch with Fall Control, the player needs to first do the same as without Fall Control, plunge attacking another ledge mid-fall. Afterwards though no further inputs are required, the player simply needs to let the character fall while being in the plunge animation. If the fall is not too high (as in, the plunge animation hasn't ended yet), all fall damage will be entirely negated. In fact, trying to move mid-air will cancel the plunge animation and lethal fall damage will be applied upon hitting the ground (though a standard Fall Control quitout could still be performed in that case). This glitch has the advantage over ordinary Fall Control quitouts though that no quitout is required and as such can be used to survive lethal falls that end on unstable ground such as elevators.
//youtube.com/watch?v=5RstnlGJPzk