Craft
From Kerbal Space Program Wiki
A craft or vessel is a group of parts which is controlled by a command module. A craft may be manned and can be categorized as a rocket, launching vertically usually on the launch pad, or as a plane starting horizontally usually on the runway. There are also spaceplanes, which are planes which can achieve an orbit. Another type are single-stage-to-orbit (SSTO) which don't stage. Usually spaceplanes are designes as SSTOs.
There are various craft already build by the developers called stock craft.