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.
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.