well yes, there are many definitions what it is. i don't think it is just playing the scales and sweeps as fast as 'you' can, cause this may be only 100 bpm at sixteenth notes. i think is starts somewhere at a certain speed. for example at 150 bpm (sixteenth notes) this would be 10 notes per second. well thats what i would say.
others told me its "being able to play everything you like without technical limitations"... when you know all the techniques and can concentrate on what you play.