[from ‘case modification’]
1. Originally a kind of hardware hack on a PC intended to support overclocking (e.g. with cutouts for oversized fans, or a freon-based or water-cooling system).
2. Nowadays, similar drastic surgery that's done just to make a machine look nifty. The commonest case mods combine acrylic case windows with LEDs to give the machine an eerie interior glow like a B-movie flying saucer. More advanced forms of case modding involve building machines into weird and unlikely shapes. The effect can be quite artistic, but one of the unwritten rules is that the machine must continue to function as a computer.