Sadie Belly Dance move question?

That is an abdominal flutter or a stomach flutter. I wouldn't put much importance on the name though since bellydance has no common terminology. You may find it under other names as well. It is considered a more advanced bellydance move and is generally taught and practiced in an intermediate course while an advanced course generally works on perfecting it and layering it in combinations. There are online instructionals via youtube and written web descriptions if you are interested in learning it and do not have an instructor however I would highly recommend an actual live instructor to demonstrate and give feedback.