Reinforcement
Any consequence that makes the behavior it follows more likely to happen again.
What it means
Reinforcement is the process, central to operant conditioning, by which a consequence following a behavior increases the probability that the behavior will recur. It comes in two forms that both strengthen behavior: positive reinforcement adds a desirable consequence (a reward), while negative reinforcement removes or avoids an aversive one (relief), and both are sharply distinguished from punishment, which decreases behavior. A reinforcer is defined functionally, by its effect on behavior rather than by whether it seems pleasant, so what reinforces one person may not reinforce another. The timing and pattern of reinforcement matter enormously: immediate reinforcement teaches faster than delayed, and the schedule of reinforcement shapes how persistent the behavior becomes. Counterintuitively, intermittent reinforcement—rewarding a behavior only sometimes and unpredictably—produces responding that is far more resistant to extinction than continuous reinforcement, which is why variable rewards are so habit-forming. Reinforcement underlies habit formation, skill learning, addiction, and the engagement loops of apps and games. It matters because it is one of the most basic and powerful mechanisms by which environments shape what organisms do.
Examples
A rat that presses a lever and receives food presses more often; a child whose tantrum is rewarded with a toy throws more tantrums—both behaviors reinforced by their consequences.
Pulling to refresh a social feed sometimes returns something good and sometimes nothing; that unpredictable payoff keeps thumbs flicking long after a predictable, every-time reward would have gone stale.
The car's seatbelt chime stops the instant you buckle up, and it is that relief, not any reward, which reinforces buckling before you pull away.
First described in Edward Thorndike (law of effect); B. F. Skinner.