VAC. Valve Anti Cheat.
Definition of cheat
transitive verb
1
: to deprive of something valuable by the use of deceit or fraud
2
: to influence or lead by deceit, trick, or artifice
3
: to elude or thwart by or as if by outwitting <cheat death>
intransitive verb
1
a : to practice fraud or trickery
b : to violate rules dishonestly <cheat at cards> <cheating on a test>
2
: to be sexually unfaithful —usually used with on <was cheating on his wife>
3
: to position oneself defensively near a particular area in anticipation of a play in that area <the shortstop was cheating toward second base>
cheater noun