What does "art-animation-run speed" stand for, exactly?

In the object editor, you can set the "art-animation-run speed" to a certain value for each unit. I know this value is model dependant and the game uses it to set the animation speed so that the unit doesn't "slide" on terrain. However, what exactly does this value stand for? The distance a unit travels in one walk animation loop, the distance it travels in one second at 1.0 animation speed, or what?

The speed a unit should move before using the run speed? At least that concept seemed to work for me, I even tested with pitlord model + run speed bonus and a preset speed designed so the pitlord only gets to that speed if with the bonus and it only used the run animation when he moved with the speed moved