Java Applets are small applications written in the Java programming language that can be embedded in web pages. They run in a web browser and require the Java Runtime Environment (JRE) to function. Applets are designed to provide interactive features, such as animations or games, enhancing the user experience on websites. However, the use of Java Applets has declined significantly due to security concerns and the rise of modern web technologies like HTML5 and JavaScript. Most web browsers have phased out support for applets, making them largely obsolete in today's web development landscape.