Software

Plug-in (computing), a piece of software which enhances another software application and usually cannot be run independently.
- Browser extension, which modifies the interface and/or behavior of web browsers
- Add-on (Mozilla), a piece of software that enhances and customizes Mozilla-based applications
Expansion pack, an add-on for a video game

Hardware

Peripheral, an optional computer hardware component that supplements or enhances the functionality of the original unit
Video game accessory, a piece of hardware used in conjunction with a video game console for playing video games

Other

An extension to a house
Addon, a person named in the Hebrew bible
An adjuvant therapy, an add-on therapy to existing treatment

See also

Category