A bit of internet jargon, strangely ignored by the Jargon File. The carbon community is all the people who you interact with in meatspace. The meaty avatars roaming the big blue room. It's everything E2 isn't -- whatever that is.
From the English words carbon, one of the basic molecules of biological life, and Community, referring to a group of people who interact over an extended period of time.
See also: F2F, Face to Face, Wetware, Real life, and RL.