1) Operant responses that may vary in topography but produce the same or similar consequences. For example, saying "Please open the door" and physically opening the door are members of the same response class if both result in an open door.

2) A collection of individual responses that have common sources of influence in the environment. Also called a behavior.

3) A set of responses that either (a) are similar on at least one response dimension, (b) share the effects of reinforcement and punishment, or (c) serve the same function (produce the same outcome).