What is the name of the force exerted by a fluid on objects immersed in it?

The name of the force exerted by a fluid on objects immersed in it is known as buoyant force. Buoyant force is always directed upwards; it is the force that opposes the weight of the immersed body. This force is equal in magnitude to the weight of the fluid displaced.

Buoyant forces emanate from the pressure exerted on the object by the fluid. They are always present whether an object is floating on the fluid or immersed in it. Since the pressure of fluids increases with depth, it follows that an object that is totally submerged in a fluid experiences greater pressure than a floating object.