An S-Delta (S∆) is a stimulusStimulus is defined as any change in the environment or... in the presence of which a specific behaviorBehavior refers to any activity or action that living o... will not be reinforced. It signals to the learner that a particular responseA response is a single occurrence or instance of a... will not result in reinforcementReinforcement is a fundamental concept in Applied Behavior A..., indicating that the behavior is not appropriate or effectiveEffective refers to one of the seven dimensions of ... in that context.
Example
If a child asks for candy when a parent is in the kitchen and typically receives the candy, the presence of the parent in the kitchen acts as a discriminative stimulus (SD) for requesting candy. However, if the child asks for candy when the parent is reading in the living room and never gets candy in that situation, the parent in the living room becomes the S-Delta for requesting candy, signaling that the behavior will not be reinforced in that context.