A rat presses a lever, a child shares a toy, a manager raises her voice in a meeting. Behavior is any observable action or reaction of an organism. Psychology treats it as the primary data for understanding mind and environment.

Some behaviors are reflexive; most are shaped by learning, goals, and context. Behaviorists once insisted that only external actions mattered; later approaches restored the role of thoughts and feelings while still measuring what people and animals actually do. Frequency, intensity, duration, and latency provide quantitative handles.

Interventions aimed at changing behavior—habit formation, therapy, organizational incentives—succeed when they alter the contingencies that maintain the action. Description comes before explanation: careful observation of when and where a behavior occurs often reveals the levers that can modify it. In that sense, behavior remains both the starting point and the final test of psychological ideas.

• Observable actions and reactions
• Shaped by learning and context
• Measured in frequency, intensity, and timing
• Target of most practical interventions