For a three-letter word, "mod" can mean an awful lot of things. The term is almost always connected to videogaming, but within that realm, it refers to adjustments made to hardware or software, ranging from the relatively simple to the breathtakingly complex.
Ben Heck got famous by taking game consoles and rebuilding them into something new - often, portable versions of what were supposed to be stay-at-home systems. Others have done the same. His website showcases, among many other things, an Atari that a reader tucked into a small, elegantly crafted wooden case.
Putting old parts in new boxes is a common hardware modding theme. Modders stick PCs and game systems into all sorts of stuff; old toys, especially those with a sci-fi theme, are a favorite. A PC gets transferred into a remote-control Batmobile, or a Mac Mini is placed inside the Millennium Falcon.
Other hardware mods serve more practical purposes. Techies who bump up their computers' speeds (it's called overclocking) need to compensate for the machines' increased heat output by building better cooling mechanisms, which can range from intricate assemblies of metal piping to enormous fans that resemble those of a jet engine. More simply, some modders just apply a little spray paint to their PC's case for a more badass look.
Hardware modding is not without its risks. Many mods - particularly those that involve cracking open a computer or console's case - will void your warranty.
Bored with your old computer game? Say, for example, you're tired of Battlefield 1942's World War II setting. So download the Battlefield Pirates mod for a more swashbuckling experience, matey.
You usually have to have the original software for such a mod to function, but the mods themselves - created by other developers or members of the public - are typically free, and can involve anything from a full-on replacement of the original game's art and audio, to unofficial patches that repair bugs, to expansions of a game's universe for extended play.
As with hardware modding, legal issues can come into play. Some companies look at mods as copyright infringement; others welcome the increased fan involvement and build mod-friendly features into their games.