This is something I find myself writing about a lot (here, here and here)
In a lot of those articles I refer to Kevin Kirby’s excellent video and you really can’t go past it for a description and an explanation:
It is a common finding, commonly associated with overpronation and also commonly confused with a medial heel whip. There is a lot of confusion between the abductory twist and the medial heel whip, especially in social media commentary. They are not the same thing. They are two very distinct and different phenomenon. The abductory twist is what is in the above video. A medial heel whip is something that occurs after the foot is off the ground.
I have actually given up responding in social media to those who are confused between the two. Move on.