Thanks for the nice comments
Gamma is simply a value or formula that defines an output change relative to an input...
So, with respect to displays it mean the display output is changed relative to the input, based on a formula.
Charles Poynton's FAQ is a good resource for info: http://www.poynton.com/GammaFAQ.html
The Gamma Curves we refer to here are for use in-camera, so change the image output from the camera compared to the scene being captured.
Mob Boss at Light Illusion