A program written using the Java programming language, which can be accessed through a Web page and downloaded to the client machine where it is run within the Web browser window. Java applets can add dynamic functionality to static Web pages provided users view these pages with a Java-enabled Web browser.
When an applet is created, its Java statements are compiled into an intermediate pseudo-machine-code language called a bytecode. The bytecode file is stored as a class file on a Web server like Microsoft Internet Information Services (IIS), and a Web page can reference the class file using an <APPLET> tag.
When a Web browser requests the page and encounters the <APPLET> tag, the bytecode in the class file is executed in a Java virtual machine on the browser.