An Acronym with far too many different meanings:

Packet Over Sonet

See RFC:1605 for more information.

Point of Sale

Point of Sale software can usually be found under "finance" in your package system.

Part of Speech

Part of Speech tagging is a standard task in natural language processing.

Piece of Shit

Commonly seen in aggravated situations when something doesn't work (correctly).

lib/main.php:944: Notice: PageInfo: Cannot find action page

lib/main.php:839: Notice: PageInfo: Unknown action