ergospheren.

1970 Physical Rev. Lett. 25 1596/1 Roger Penrose has pointed out a way to extract energy from a black hole endowed with angular momentum. It makes use of the ‘ergosphere’.., the region between the horizon..and the surface of infinite red shift (coincident with the horizon only for case of the angular-momentum-free Schwarzschild black hole).

1971 Ruffini & Wheeler in Moore & Hardy Significance of Space Res. for Fund. Physics 87 A particle that has come into the region between surfaces (1) and (2) (‘ergosphere’) can still, if it is properly powered, escape again to infinity.

1978 J. M. Pasachoff & M. L. Kutner University Astron. xii. 327 An object can be shot into the ergosphere of a rotating black hole at such an angle that, after it is made to split into two, one part continues into the event horizon while the other part is ejected from the ergosphere with more energy than the incoming particle had.

1989 C. Will in P. Davies New Physics ii. 26/1 For the Kerr solution, rotation of the black hole produces the same dragging... The region inside which the dragging effect has this property is called the ergosphere.