1) Any behavior that prevents a negative reinforcer from occurring.

2) The prevention of an aversive stimulus by a response. In deletion procedures, the response cancels presentations of the aversive stimulus; in postponement procedures, the response only delays presentations. In discriminated, discrete-trials, or signaled avoidance, an exteroceptive stimulus (sometimes called a wariii?ig stimulus) precedes the aversive stimulus; a response during this stimulus prevents the aversive stimulus on that trial. If no response occurs and the aversive stimulus is presented, escape from it typically depends on the same response that is effective for avoidance. In cotitinzious, free-opera?tt, or Sidman avoidance, no exteroceptive stimulus is arranged and, typically, there is no provision for escape. Each response postpones the aversive stimulus (usually, brief shock) for a fixed period called the response-shock (RS) interval; in the absence of responses, shocks are delivered regularly according to a shock-shock (SS) interval.

3) Avoidance describes a performance which increases in frequency because it postpones the appearance of an aversive stimulus. In the classical laboratory experiment, a rat postpones an electric shock for a brief interval each time it presses the lever. If the rat presses the lever frequently enough, .it avoids the electric shock. Avoidance is to be contrasted with escape, when the performance actually terminates the aversive stimulus.

4) Behavior which reduces or eliminates stimuli which in the past have been followed by punishment. The punishment then, does not occur. Avoidance is different from escape we get out of punishment that has already started. For example, we avoid a traffic jam by taking an alternate route before we get in the jam, whereas we escape from a traffic jam by taking an alternate route after we have already gotten caught in the jam.