Body Manipulation is an ability that allows the user to freely manipulate his/her own body structure.
As ghosts, the former Guardians of Earth have the ability to liquefy, which they used to wrap Kami in order to prevent him from escaping. Majin Buu and his various incarnations (Super, Kid, etc.) have complete control over every aspect of their physical makeup, allowing them to able to stretch, shapeshift, liquefy, and otherwise manipulate their malleable body; useful as both an attack and defense and as a tool in absorption. This capability also aided them in several of their more deadly attacks, including the Wrap Attack and the Elastic Tentacle.
After being drenched and deformed by the Culture Fluid, Bio-Broly became malleable enough to twist his head 180 degrees and stretch his own neck.
Finally, Baby could liquefy his own body and take the shape of a ball, the former of which aiding him greatly in possessing others' bodies.