What is "convertiplane"

n. Any of several forms of aircraft capable of both vertical takeoff and landing, and of normal forward flight; usually has variable geometry wings that can rotate

A convertiplane in popular usage is an aircraft that converts in flight to change its method of obtaining lift. The FAI define it more narrowly as an aircraft which uses rotor power for vertical takeoff and landing ( VTOL) and converts to fixed-wing lift in normal flight. This is the definition used here.