A jack-up rig is a type of mobile platform that is able to stand still on the sea floor

Seabed

The seabed is the bottom of the ocean.- Ocean structure :Most of the oceans have a common structure, created by common physical phenomena, mainly from tectonic movement, and sediment from various sources...

, resting on a number of supporting legs. The most popular designs use 3 independent legs, although some jackups have 4 legs or more. On "mat-type" jackups the legs are connected to a submerged hull.
A jackup is a floating barge fitted with long support legs that can be raised or lowered. The jackup is maneuvered (self-propelled or by towing) into location with its legs up and the hull floating on the water.