Here's the definition of "Operating Thetan" from the 'Scientology Technical Dictionary', 1975:
"OPERATING THETAN, 1. a thetan exterior who can have but doesn't have to have a body in order to control or operate thought, life, matter, energy, space, and time. 2. willing and knowing cause over life, thought, matter, energy, space and time. And that would of course be mind, and that would of course be universe. 3. an individual who could operate totally independently of his body whether he had one or didn't have one... this state is being attained by drills and familiarity after the state of Clear has been attained."