The term "keydown" refers to an event in computer programming that occurs when a key on a keyboard is pressed down. This event is commonly used in web development to capture user input, allowing developers to create interactive applications. When a key is pressed, the browser can detect which key was activated, enabling actions like typing text or controlling game movements. In the context of web applications, the JavaScript programming language often handles keydown events. Developers can use functions to respond to these events, such as triggering animations or validating form inputs. This enhances user experience by making applications more responsive to user actions.