A self-elevating (or jack-up) unit is a floating unit which is designed to operate as a sea bed-stabilised unit in an elevated mode. These units have a buoyant hull (generally either triangular or pontoon shaped) with movable legs capable of raising its hull above the surface of the sea. The legs may be designed to penetrate the sea bed, or be attached to a mat or individual footings which rest on the sea bed. These unit types are generally not fitted with a propulsion system.
Source: Rules and Regulations for the Classification of Mobile Offshore Units, Part 3, Functional Unit Types and Special Features, June 2013, Lloyd’s Register, Global Standards