Meaning Point of contact
Type Acronym
Popularity ★ ★ ★ ★ ☆  Common
Usage General (not just online)

Refers to the person you are supposed to meet or check in with at a location, or who you are supposed to communicate with via email; often displayed on business proposals and marketing materials.

Updated February 14, 2013
Meaning Piece of crap
Type Acronym
Popularity ★ ★ ★ ☆ ☆  Average
Usage Online Only (chat, messaging, e-mail)

A milder version of POS; sometimes refers to a piece of junk, but may also used as an exclamation towards someone else, i.e., in online gaming, when someone sneaks up behind you and kills your character, you might type, "POC!"

Updated December 26, 2013
Meaning Proof of concept
Type Acronym
Popularity ★ ★ ☆ ☆ ☆  Uncommon
Usage General (not just online)

A proof of concept is a demonstration of how an idea or theory will work. For example, a POC may be presented by a business sales team to show how their product will fit a need or solve a problem.

Example "They really liked our POC demo."
Updated January 22, 2013
Information from PC.net