An interesting coincidence allowed early engineers to avoid some complexity in home television receivers. When TV pictures were first sent by radio, noise caused by radio and other electronic interference was most visible in the darkest parts of the image, a situation made worse by the human eye's greater contrast sensitivity in darker areas of a scene. So, the signal was processed before transmission to have brighter shadows, and made normal again in the receiving TV, reducing the noise significantly.
One of the great coincidences of broadcast television engineering is that the behaviour of the cathode ray tube in classical television receivers happened to almost exactly reverse the brightening of shadows in the camera, so no extra electronics was required in TVs to implement gamma processing. Modern TFT-LCD and OLED displays behave very differently, but the processing electronics to simulate the old approach is now trivial.
For most of the history of TV, there was only one or two ways of handling this situation - one or two ways to encode brightness. Modern cameras, though, have introduced manufacturer-specific brightness encodings designed to make better use of the particular characteristics of that camera's sensor. At the same time, updated ways to send TV to viewers in the home, particularly including HDR, have driven the development of even more ways to describe just how bright a pixel on the screen should be. There are now often several per camera manufacturer, and equipment including displays and grading software must often be told what to expect, or the picture will look too bright, too dark or with incorrect contrast.
The term gamma comes from the lowercase Greek letter, γ, used in the mathematical equation representing the in-camera picture processing of gamma correction. In this equation, the recorded brightness value L is raised to the power gamma, Lout = Linγ, creating an exponential curve. Few actual "gamma" processing devices actually work in such a literal manner, although the mathematics they use generally approximate the shape of an exponential curve.