Negative reinforcement can best be defined as:

Negative reinforcement is a concept in behavioral psychology that involves the removal of an undesirable stimulus in order to increase the likelihood of a desired behavior being repeated. By removing something unpleasant, a person is motivated to engage in a behavior that will result in that unpleasant element's removal.

For instance, if a student studies hard to avoid the stress of failing an exam, their studying is reinforced by the absence of stress. Thus, they are more likely to study in the future to avoid that negative outcome. This process highlights how negative reinforcement is fundamentally about encouraging desired behaviors through subtraction of negative stimuli, rather than the introduction of new penalties or consequences.

This understanding distinguishes negative reinforcement from punishment, which aims to decrease behavior by adding adverse stimuli or additional penalties.