A supplement to a piece of software that gives an added layer of functionality: for example, add-ons in Mozilla Firefox can allow you to take pictures of the screen or remove adverts.

"additional component," 1941, from add (v.) + on.

In charge accounts, the purchasing of additional merchandise without paying in full for previous purchases, especially in installment-credit plan selling.

Refers to a product designed to complement another product. For example, there are numerous add-on boards available that you can plug into a personal computer to give it additional capabilities. Anoth [..]

1 : being or able to be added on [ no-fault benefits] 2 : able to be added to [ certificates of deposit]

any component of a package tour that is not included in the package price Advanced ecotourism:

An extra, optional service that travelers can purchase during the bookings process.

A selection, typically at an increased price, added to a travel reservation.

An add-on is a software extension that adds extra features to a program. It may extend certain functions within the program, add new items to the program's interface, or give the program addition [..]

A transaction that adds related equipment to an existing lease. Typically, this term is used when the new equipment is financed using the same lease structure (i.e., Fair Market Value, $1.00 Purchase [..]

A transaction to add related equipment to an existing lease. Typically, this term is used when the new equipment is financed using the same lease structure (i.e, Fair Market Value, $1.00 Purchase Opti [..]

Equipment leasing transaction that adds related equipment to an existing equipment lease. The term is used when additional equipment is financed using the same terms as the original transaction, such [..]

(n) a component that is added to something to improve it(n) a supplementary component that improves capability

An individual who holds a teaching license may add an endorsement in specific areas to his/her license.

 An add-on is a software extension that adds extra features to a program. It may extend certain functions within the program, add new items to the program's interface, or give the program additional capabilities.  

see plug-in.

An amount used only with specified/published international fares for the construction of constructed/ unpublished international fares. (Also referred to as an arbitrary or proportional fare.)

A Python distribution that uses Pyramid's extensibility to plug into a Pyramid application and provide extra, configurable services.

Special services, arrangements, or accommodations made in addition to the basic service provided by an airline, hotel, or other operator in the travel industry.

A chance to buy more chips. Comes at the end of the re-buy period during a multi-table tournament (MTT), normally after 60 minutes.

Some tournaments allow players to add more chips to their stack during certain periods, usually at the beginning of a tournament or a new round.

In tournament play an opportunity to purchase additional chips regardless of your chip stack. This is usually offered only once after the first break/end of the rebuy period. The add-on usually offers more chips per dollar than the original buyin and rebuys.

An option, usually at extra cost, added to travel arrangements. Adjoining rooms-

An optional tour, excursion, etc., usually at extra cost, added to travel arrangements.

An optional extra that a customer can add to their basket during the booking process and add value to a tour or activity. For instance, a video package or audio guide. Here are 8 add-ons you can give [..]

any component of a package tour that is not included in the package price

  any component of a package tour that is not included in the package price  

Add-on may refer to:

Add-on is the Mozilla term for software modules that can be added to the Firefox web browser and related applications. There are three types: extensions, themes, and plug-ins. Mozilla hosts them on it [..]