Not being ignorant at all
It does have to do with both actually LOL but for my workout I was referring to your abs... let me see if I can find Bunny's reply about them as she described them better then I did a few pages back...
"To elaborate on the vac's...pull your belly muscles in tight and flex them, like you were sucking in really hard... only you have to breathe then release the breath while still holding the abs in, and squeeze them for anywhere 10-15 seconds when just starting." ~Bunny