n.)
1. Short for "modification". Used mainly to describe either add-ons to a modular device, extra files being added (more often than not unofficially) into a program or game, or sometimes a physical object going into a jury-rig.
2. Short for "moderator". Used mainly in online forums, chat rooms, chat servers, and games to describe a person or bot who oversees activity in the environment to help newbs and punish trolls.
3. Acronym for "Manager On-Duty". Retail worker lingo for an active manager, mostly used through walkie-talkie radios to call for a manager to request assistance, and to either mask the request for a manager or sound more professional to the customer.

1. Having a message get deleted or edited.

Man on duty - a guy out with a bunch of girls, obligated to take on all manly responsibilities.

To modify something. Usually refering to to the technically inclined

COMPUTING .MOD is a file extension and a shortname for an Amiga Module.
4 channels, stereo, sampled instruments.
And it has a pure oldschool sound.

Multiplexed Optical Data Storage or MODS. It is a storage unit which can potentially store up to one terabyte (1,000 gigabytes) of data on one standard-size disc. MODS will be laser-based like DVDs, CDs and the new Blu-ray system but uses much more subtle variations in the way light reflects from the discs. Where existing schemes have patterns of pits that reflect the laser as a series of ones and zeros, MODS can encode and detect more than 300 variations per pit. After error correction and encoding, this leads to 10 times the data density of Blu-ray Disc, currently the record holder for consumer optical storage.

To mod is to break something partially so that it still works for at least part of its original uses.