the soft fleshy flap o' skin that hangs down from the upper arms of old people and shimmers and shakes under the slightest movement of the rest of the body
Lets say a group of lads standing outside a.... i dont know, a tyre Warehouse saw a fit lass walking past, they might say "check out the flappage"in order to bring everyones attention to the fit lass.
Or you could say, "i got some bwad flappage last night" meaning you had some vinga action.