belly landing

Noun

 * 1)  A landing of an aircraft without the landing gear being deployed.

Usage notes
"Belly landing" is often restricted to emergency landings where the pilots knowingly land the aircraft with the gear retracted, due to gear extension being impossible or inadvisable (for instance, in a water ditching); in this system, a landing where the pilot(s) merely forget to extend the landing gear of an otherwise-serviceable aircraft is termed a gear-up landing.