Short takeoff and vertical landing
Carriers intended for STOVL aircraft may have "ski jump" ramps, as used on current British, Indian, Russian and Spanish vessels. By making a short takeoff roll up a ramp, the aircraft can take off with more energy and a heavier load.
U.S. amphibious warfare ships that carry U.S. Marine Corps STOVL aircraft, such as the current AV-8B Harrier II and future F-35B Lightning II, do not use ski jumps. The principal reason is that this gives more deck space for VTOL helicopters and MV-22 Osprey tilt-rotor aircraft.
Different kinds of interservice politics may be involved in not having the ski jump. From a cynical Marine perspective, it gives them confidence that the Navy will not take its amphibious assault ships as general-purpose aircraft carriers. From a cynical Air Force perspective, the Navy will not be able to have more decks that can handle the higher-performance F-35C Lightning II.