Female Edison to male stage pin connector adapter. (Note that this nomenclature breaks the long standing tradition of the MALE END always being specified FIRST on adapters; should be called a "Male stagepin to Edison adapter".)
http://www.stagelightingstore.com/Female-Twist-Lock-nub-in-to-Male-3-Pin-adapter?sc=25&category=279852
Also note that to be fully-compliant with NEC 520.69(A) "No reduction in Current Rating," the adapter's female must be of the neutral "T-slot" 15/20A Edison female (NEMA 5-20) type: and not a "regular" Edison NEMA 5-15. Thus what is pictured above is not truly code-compliant.
For more, see this thread.
http://www.stagelightingstore.com/Female-Twist-Lock-nub-in-to-Male-3-Pin-adapter?sc=25&category=279852
Also note that to be fully-compliant with NEC 520.69(A) "No reduction in Current Rating," the adapter's female must be of the neutral "T-slot" 15/20A Edison female (NEMA 5-20) type: and not a "regular" Edison NEMA 5-15. Thus what is pictured above is not truly code-compliant.
For more, see this thread.