A term that is used for a Scene girl's vagina. It originated as both Jellyfish and Cupcakes are cute things that Scene girls can often randomly refer too. However, They also both have qualities that can be related to a vagina. A Jellyfish being wet, sometimes smelly with many squishy parts, and a cupcake as it's small, harmless and delicious.
Man, I would love to pound her Jellyfish-Cupcake!