An abductory twist or medial heel whip is the sudden movement of the heel medially or abducting just as the heel comes off the ground during gait. The usually occurs when the leg is externally rotating and the foot is pronating. Friction from the ground usually prevents the abduction or medial whip, but as soon as the heel off-loads, friction can no longer hold the foot and the heel suddenly abducts. This video explains it well:
The abuctory twist is more of a sign as opposed to something that needs treating. Usually there is an underlying problem causing this medial heel whip that needs to be addressed. When that is treated the ‘whip’ or the abduction generally always comes right on its own. There is a really good discussion on it here and review of its pathomechanics here. There is some opinion that there are proximal problems that cause this and strengthening exercises are needed to correct it.