Rigid body

Rigid bodies are the way to have dynamic interations with the fluid (other then changing the velocity field directly)

Static bodies

Static bodies act on the fluid, but the fluid doesn’t act on the fluid. This is called a weak coupling between the rigid body and the fluid. They have a velocity that is imparted on the fluid. Think of motorized objects pushing through the fluid.

Dynamic bodies

Dynamic bodies are affected by the fluid. They can also in turn, affect the fluid, which is called a strong coupling with the fluid.