How much a girl's ass jiggles when you slap it. If a girl has a nice ass and it is not stiff it will jiggle a lot compared to a girl who has a small ass which is stiff.
Man, did you see the ass on that girl? I bet she has a prettyhigh jiggle factor
When your desk is wobbling to much during your class and causing problems for classmates. The Jiggle Factor of an object is how much the object wiggles and wobbles during intense periods of concentration.
"My desk had a Jiggle Factor last class it was pissing me off"
"Lets measure it"
"I don't know how "