In Java, an applet is a small application that is designed to be embedded within a web page. Applets were particularly popular in the early days of the internet when browsers supported Java applets as a way to add dynamic and interactive content to web pages. However, their usage has declined significantly due to security concerns, and modern web browsers no longer support Java applets.

Here are some key points about Java applets:

Embedding in Web Pages: Applets were typically embedded in HTML pages using the <applet> tag. Users could view and interact with the applet directly within their web browsers.

Java Applet Life Cycle: Applets follow a life cycle similar to standalone Java applications. They have init, start, stop, and destroy methods that are called at various points during their execution.

Security Concerns: Java applets were executed within a restricted environment called the "sandbox" to prevent malicious activities. However, security vulnerabilities in Java applets led to a decline in their usage, and major web browsers have since removed support for the Java browser plugin.

Replacement Technologies: As a result of security concerns and the evolution of web technologies, alternative technologies such as JavaScript and HTML5 have become more popular for creating dynamic and interactive web content.

Deprecated in Java: With the release of Java 9, the browser plugin mechanism, which was used to run Java applets, was deprecated. Java applet support has been removed in more recent versions of Java.