What does the mouse-binding “in-between move” do?

Soo, changed my settings around a bit so that Shift-C is cursor-to-selected and Ctrl-S is "view all without moving cursor". After doing this I had some intermittant trouble with the view resetting with the original Shift-C action when I alt-tabbed or used my screenshot program.

I finally tracked it down today; somehow this got set instead of disabling the original command:

I can't find "In-between Move" anywhere else in the key list; though that might be because search dosen't seem to work on it:

Note that the box dosen't become red like you typed something invalid in it.

Sooo ... what is this mouse action supposed to represent, anyway? I can't consistantly do it, so I'm not positive what it is, but I guess it has something to do with dragging between windows?

In-between Move corresponds to blenders Event.type of value 'INBETWEEN_MOUSEMOVE'.