Reaction time is the duration it takes for a person to respond to a stimulus. This can involve physical actions, such as pressing a button when a light turns on, or cognitive responses, like recognizing a sound. Reaction time is influenced by various factors, including age, fatigue, and the complexity of the task. Measuring reaction time is important in fields like sports and psychology. For example, athletes often train to improve their reaction time to enhance performance. Additionally, understanding reaction time can help in assessing conditions like ADHD or dementia, where response speed may be affected.