I think most instructors will agree that it is shrimping. Hip Movement. Were you looking for a more exciting answer?
The Gracies teach that the art of Jiu-Jitsu is about defense. Jiu-Jitsu means “gentle art” in Japanese. It means being able to defend yourself vs. a larger and stronger attacker.
In the beginning of your training, you are going to be on defense most of the time. Your biggest obstacle is to learn to not try to lift, push, or pull your partner out of position using strength. Your job is to learn to keep your arms close, defend your neck, and move your hips to get yourself out of trouble so you can start to improve your position and eventually go for a submission.
When you become more advanced, hip movement is key to setting up submissions. From the guard, you move your hip to open up opportunities for sweeps and submissions. From the top position, you’re moving your hips.
I can still hear Rigan Machado yelling at me during training, “Scape your hip Ryan! Scape your hip!!!”
Simple but not easy!