Lun (name of the kaspian sea monster) is a combat missile craft.
WIG is an abbreviation of Wing-In-Ground effect. A WIG craft can be seen as a crossover between a hovercraft and an aircraft. It flies just above the surface, usually the water surface therefore others use the term WISE or WISES (Wing In Surface Effect Ship).
A hovercraft is floating on a cushion of air that is created by a fan that blows in a cavity under the hull. The cavity is bounded by so called skirts, rubber curtains that restrict air leakage and more or less seal the cavity. The air curshion reduces the friction drag of the hovercraft with the water which would make it a very efficient vehicle if is wasn't for the fan that creates the cushion. A WIG craft also sits on a cushion of air, but this cushion is created by aerodynamics. This means that it only exists when the WIG craft has sufficient forward speed. This is called a dynamic air cushion as opposed to the hovercrafts static air cushion. You can compare this to the relation aircraft-helicopter, the aircrafts wings generate lift because of their forward speed, whereas the helicopters rotor has work continuously for generating lift.
A WIG craft is especially designed to take advantage of the benefits of ground effect. Therefore a WIG vehicle will always fly close to the surface. Although it is called ground effect, most WIG vehicles only fly over water, but some are amphibious.