a Java application; an application program that uses the client's web browser to provide a user interface
"The applet loaded in my web browser allowed me to check flight status without opening any other software."
a small program module that runs under the control of a larger application, typically a web browser
"The Java applet loaded in my web browser allowed me to play an interactive game without downloading any additional software."
In plain English: An applet is a small, self-contained program that runs inside another application to perform specific tasks without needing to be installed separately.
"The applet lets me set an alarm on my phone without opening any other programs."
Usage: An applet is a self-contained Java program designed to run within a specific host environment like a web browser. Unlike standalone applications, it operates with limited privileges and relies on the parent application for its execution context.
The word applet combines the root of app with the diminutive suffix -let to indicate a smaller version. Its usage was likely further popularized by its association with the company Apple and their scripting language, AppleScript.