A Java Applet is a small application written in the Java programming language that can be embedded in a web page. It runs in a web browser and provides interactive features, such as animations or games, without requiring users to install additional software. Applets are designed to be platform-independent, meaning they can run on any operating system that supports a compatible browser. Java Applets use the Java Virtual Machine (JVM) to execute code, ensuring security and portability. However, their use has declined due to security concerns and the rise of modern web technologies like HTML5 and JavaScript, which offer similar functionalities without the need for a plugin.