A 'motion' is a written petition. It means to file a petition that requests something from the court, with the Clerk of the Court's office, which will be presented to judge for his consideration.
"Motion" isn't a word officialy used in (European) courts (and I can't see its utility in American courts either). A motion is an idea or proposition that is brought up for discussion before a group....
I'm pretty sure it means the motion or movement that is going to happen. So, if you apply force in a direction to a box, the impending motion will be sliding or tipping in the direction of force...