A plane is a craft which starts horizontally and utilises the lift generated from wings or winglets. Because planes usually use jet engines they are more efficient than rockets but normally don't leave the atmosphere. On one side this is useful as it continues to generate lift with wings but on the other hand does the atmosphere induce drag at all times preventing an stable orbit.
Planes are build in the Space Plane Hangar and start from the runway. It is possible to build planes in the Vehicle Assembly Building but from this building planes would start on the launch pad. But this place is to short to accelerate and generate enough lift to start there. There are various stock planes available in the Space Plane Hangar.
The currently fast plane moved at about 2340 m/s relative to the ground a bit short of Mach 7. At this speed it is possible to circumnavigate Kerbin in about 29 minutes at an altitude of 40 km. For comparison the speed required to orbit Kerbin at 70 km (outside the atmosphere) is only 2296 m/s.
- “The MachingBird Challenge!” in the forums.