TLGI

[derekleffew]

Twist Lock Ground In. Old term for NEMA L5-15 or L5-20. The bend on the ground blade turns in.

http://www.42u.com/netbotz-amp-detector-module.htm

From http://www.lightfool.com/features/connectors/index.html :

L5-20 "Nub-In Twist" 20A 125V 2-Pole 3-Wire Grounding
Commonly found in school theatres wired after 1981, it's used in place of 20A 2P&G "Stage Pin" plugs where a 125V locking connector is desired and generally replaces the "Nub-Out twist" connector.

See also TLGO.