A small program that runs on a web browser and enhances interactivity is commonly referred to as a web applet or JavaScript application. These programs can execute in real time within the browser, providing dynamic content and functionalities such as animations, form validations, and interactive user experiences. By leveraging technologies like HTML, CSS, and JavaScript, web applets enhance the usability of websites, making them more engaging and responsive to user interactions. This crucial element contributes to modern web design and development practices.