Stands for Indie Rock Cred
A term denoting a fanciful score that can be placed upon nearly anything; words, actions, cars, accoutrements, styles, and - not least of which - bands.
The score denotes the amount of indie credibility that the thing brings.
Roughly speaking, lowest on the IRC scale would be the Dave Matthews Band. They represent the bedrock of the anti-indie. Calling the band "Dave" or "DMB" might be even worse.
The pinnacle of the I.R.C. scale was once thought a mythical destination. Hoping to achieve the mythical peak, many strive for a mix of the arcane with the familiar - i.e. knowing off the top of their head who produced Can's "Soon Over Babaluma." One can often view Indie Record Store clerks in their natural habitat competing for mates in this regard. Because their waifish bodies are to weak to engage in traditional forms of mate competition, they constantly attempt to one-up each other in order to reach the pinnacle of I.R.C.
Little do they know, however, that in the late 90's Mr. R.E. Brewster of 14 Exeter Avenue discovered the pinnacle of I.R.C. During the transcendent moment, Mr. Brewster - while wearing an original New York Dolls T-shirt purchased at a CBGB's Dolls show - recounted the time in 1968 he saw The Velvet Underground perform in Andy Warhol's studio. From that moment on, the mythical pinnacle was a reality.
Ironically, like most in-crowd references, one must have some IRC to even be able to accurately spot IRC.
It is also possible to achieve "ironic indie rock cred." This is when something goes so low on the scale that it swings back around to the top; i.e. a guy wearing Hello Kitty stuff and listening to the Backstreet Boys. This should only be attempted by trained professionals.
"Oh man, sportin' the Stooges shirt; some major I.R.C. there."
"I dunno guys; I think I lost I.R.C. when I bought the John Mayer album."