applet

A small program module that runs under the control of a larger application, typically a web browser.

Noun

A small program module that runs under the control of a larger application, typically a web browser.
- Holonyms: app, application, program
- If a component must run on different kinds of client systems and if the limitations imposed by sandboxing are acceptable or outright desirable, then building that component as a Java applet makes sense. - 1996, Network...
- You can also configure a hot corner to open the Expo screen, or install the Expo applet. - 2021, Richard Petersen, Linux Mint 20.2: Desktops and Administration:
Coordinate Terms: utility worklet trustlet

From app + -let, but perhaps also influenced by Apple (the term originated in AppleScript).