See WoW:AddOn for the World of Warcraft AddOn reference.
See WildStar AddOn or WildStar:AddOn for the WildStar AddOn reference.

AddOns are self-contained components that change the behavior of a program.

SummaryEdit

An AddOn for a game is generally a collection files you can put in your game folder, that can enhance interaction with the game. AddOns can perform a wide variety of tasks, including adding new buttons to the screen, altering or adding windows, replacing or adding significant functionality, or adding whole new programs.

DetailsEdit

Some AddOns can be dependent on other AddOns to work, and some AddOns can be just collections of other AddOns. Some AddOns are standalone, able to run without any additional software. Others are built on libraries. For example, in WoW, the old Sea or Ace libraries. Others such as the old WoW Cosmos addon, are compilations of many individually-developed mods or addons.