A term used to describe the amount of resilience and elasticity of an object. Usually associated with tits, but can also be used to describe a nice ass. It is always good for a woman's breasts to have a fair amount bounceability. Too little is not good. Likewise too much can be bad as well. Bounceability in any other body part is most certainly frowned upon... unless you are into that kind of shit.
Bounceability can also be used as one of several standards of measurement for boobs, and is directly related cup size, perkiness, and amplitude of motion during ANY physical activity.
A definition created by a Swedefag which basically means that you get a boner. Mostly from a girl depending on your gender. You can for example have this wet dream or just a day dream about a girl when suddenly your stick gets filled with blood and ready to go.