- a device or unit added to equipment or a construction: an add-on to a computer; a nice add-on to an old house.
- an extra charge: Add-ons for taxes and tour guide fees boosted the price of the vacation to $2,500.
- an additional item, as a rider or provision: This is just another legislative add-on.
- anything added on: a hi-fi system that can be augmented with add-ons like extra speakers.
- being installed or provided as an add-on: an add-on speaker system.
- a feature that can be added to a standard model or package to give increased benefits