Jelly On Springs 

A bouncing bum, not necessarily female.

The once was a curate at Kings
Whose mind was on heavenly things,
But his heart was on fire
For a boy in the choir
Whose ass was like jelly on springs.

Jelly On Springs by John Tzetzes May 8, 2011

jelly-on-springs

bouncing or quivering female breasts and/or buttocks

She was a bit nervous about her jelly-on-springs getting unwanted attention.

jelly-on-springs by The Return of Light Joker May 20, 2010