1) A procedure for transferring control of responding from one stimulus or set of stimuli to another by gradually removing one while the other is gradually introduced. Stimuli may be faded in or out (e.g., once a pigeon dates key colors, the discrimination may be transferred to line orientation by maintaining differential reinforcement while gradually decreasing colour intensity and increasing line intensity).

2) Disregarding the common usage of the term, fading does not always refer to the disappearance of a stimulus. Sometimes in a fading procedure, a stimulus begins at a low value and is increased in magnitude. Consider, for example, a case where a pigeon pecks (and is reinforced) when the key is red, but not when it is dark. The control by the dark key may be shifted to a green key by first projecting a faint green light on the dark key and then gradually increasing the intensity. If the rate of change of the stimuli is properly paced with the organism's behavior, the control may be shifted from one stimulus to another without any instances of the bird's pecking inappropriately.

3) the procedure by which an added stimulus (prompt) is gradually withdrawn. Fading is used to help establish a simple discrimination.

4) The gradual removal of a prompt or other help or cue for responding.