VAC

Valve Anti-Cheat. Basically, it's a program that is like a virus scanner only for hacks, if they detect hacks on server joins and whatnot, you will be banned within a few days, hours, or weeks.

Players who have been banned always claim they didn't cheat, or their brother or friend put the hacks on, basically trying to get it out. There have only been less than 10 people actually unbanned from VAC before. Anyone who is banned will only be banned from VAC secure servers, but can still play on unsecured ones. Every game that uses VAC will be inaccessible (you won't be able to play on VAC secure servers).

It's often criticized as a way to make money from Valve to get a new account and games. Accounts that have been banned payed up to thousands on games before, but over 1 hack they loose all.

Many times VAC isn't updated to the most recent hacks, private hacks still exist, and are harder to detect.

VAC has certainly busted many cheaters, but some still get by.

Valve Anti-Cheat

Technology used in Steam games like Half-Life, Counter-Strike etc. to stop cheaters and hackers. Anyone who cheats will immediately be banned from all servers running VAC.

Some think it's cheesey dance music, others think it's crappy power noise, some think it's the best thing since sliced bread.
If you haven't heard more than at least 3 Velvet Acid Christ albums, then you really aren't in a position to judge.
There are many different styles found here, including industrial, goth, electro, noise, psy-trance and "strange techno", if you are a fan of anyone like The Cure, The Sisters of Mercy, Nine Inch Nails, Skinny Puppy or just want to find something different, Velvet Acid Christ is not to be missed.

Acronym for EBM artist Velvet Acid Christ.

To be banned on a game server run by valve that is VAC secured
e.g. Tf2, CSGO, Half life, etc.

A vacuum cleaner.

Abbriviation for Vacation

Usually seen in a working environment in the form of Email. It is commonly used to notify a group of people if someone will be away from work.