What is a Mod?

A mod (short for "modification") is an alteration by players or fans of a video game that changes one or more aspects of a video game, such as how it looks or behaves. Mods may range from small changes and tweaks to complete overhauls, and can extend the replay value and interest of the game.
Modding a game can also be understood as the act of seeking and installing mods to the player's game, but the act of tweaking pre-existing settings and preferences is not truly modding.
Mods have arguably become an increasingly important factor in the commercial success of some games, as they add a depth to the original work, and can be both useful to players and a means of self-expression.
People can become fans of specific mods, in addition to fans of the game they are for, such as requesting features and alterations for these mods. In cases where mods are very popular, players might have to clarify that they are referring to the unmodified game when talking about playing a game. The term vanilla is often used to make this distinction. "Vanilla Minecraft", for example, refers to the original, unmodified game.
As early as the 1980s, video game mods have also been used for the sole purpose of creating art, as opposed to an actual game. This can include recording in-game actions as a film, as well as attempting to reproduce real-life areas inside a game with no regard for game play value. This has led to the rise of artistic video game modification, as well as machinima and the demoscene.
Popular games can have tens of thousands of mods created for them. Popular websites dedicated to modding include Nexus Mods, Mod DB, and Steam Workshop.