An event listener is a programming construct that waits for specific actions or events to occur in a software application. These events can include user interactions like clicks, key presses, or mouse movements. When the specified event happens, the event listener triggers a predefined function or response, allowing developers to create interactive and dynamic user experiences. In web development, event listeners are commonly used with the Document Object Model (DOM) to respond to user actions on elements like buttons or forms. They help manage how the application behaves in response to user input, enhancing usability and engagement in applications built with languages like JavaScript.