Short for registration. A term used for some online games that manage to lose packets in the transfer between client and server, specifically counter-strike where it is possible that a direct hit to the head (or any other part of the body) not be registered by the server resulting in no kill and agrivation. Often people get annoyed with this stupid aspect of online gaming and diol.
"I just shot that guy in the head, didn't get any rego though"
"Im so tired of this rego, when i shoot it never hits."