1. <filename extension, application, file format, music> (module) The filename extension for a sampled music file format that originated on the Commodore Amiga. A .MOD file is composed of digitised sound samples, arranged in patterns to create a song. There are .MOD players for most personal computers including Amiga, Archimedes, IBM PC, and Macintosh.
An IBM PC will require a sound card capable of handling digitised samples (Sound Blaster, Sound Blaster Pro, GUS) and slower Intel 80386-based PCs may not be able to do anything else while playing a module.
.MOD files differ from .MID (MIDI) files in that they contain sound samples. This allows each song to use different sounds but it also puts more load on the CPU than playing a MIDI file, since more data must be processed for each note. A slow CPU would benefit from a sound card with wavetable synthesis which handles samples instead of the CPU.
Module files come in various formats including .MOD. Formats evolved from .MOD include .S3M, .FAR and .669. Most contain improvements on .MODs.
2. <jargon> modify or modification.
This abbreviation is very common - in fact the full terms are considered formal. "Mods" is used especially with reference to bug fixes or minor design changes in hardware or software, most especially with respect to patch sets or a diff.