A Java applet is a small application which is written in Java or another programming language that compiles to Java bytecode and delivered to users in the form of that bytecode. The user launches the Java applet from a web page, and the applet is then executed within a Java Virtual Machine (JVM) in a process separate from the web browser itself. A Java applet can appear in a frame of the web page, a new application window, Sun's AppletViewer, or a stand-alone tool for testing applets. Java applets were introduced in the first version of the Java language, which was released in 1995.
Java applets are usually written in Java, but other languages such as Jython, JRuby, Pascal, Scala, or Eiffel (via SmartEiffel) may be used as well.
Since Java bytecode is cross-platform (or platform independent), Java applets can be executed by browsers (or other clients) for many platforms, including Microsoft Windows, FreeBSD, Unix, macOS and Linux.
Java applet technology has been marked for deprecation.