Kurt Vonnegut's Cat's Cradle is woven with a delicious vocabulary of concepts-that-ought-to-exist. Some of these have wormed their way into the broader lexicon. For this one, we might well begin with a quote (from Steven Johnson (author of Emergence: The Connected Lives of Ants, Brains, Cities and Software, though the quotation is from an article in Discover, April 2003):
A karass is a spontaneously forming group, joined by unpredictable links, that actually gets stuff doneó as Vonnegut describes it, "a team that do[es] God's Will without ever discovering what they are doing." A granfalloon, on the other hand, is a "false karass," a bureaucratic structure that looks like a team but is "meaningless in terms of the ways God gets things done."

No doubt you've experienced these two types of networks in your own life, many times over. The karass is that group of friends from college who have helped one another's careers in a hundred subtle ways over the years; the granfalloon is the marketing department at your firm, where everyone has a meticulously defined place on the org chart but nothing ever gets done. When you find yourself in a karass, it's an intuitive, unplanned experience. Getting into a granfalloon, on the other hand, usually involves showing two forms of ID.

Google tells me that 238,000 pages have some connection to Steven Johnson's invocation of the term.

theliterarylink.com offers another useful rendering, but doesn't cite Cat's Cradle:

karass: a term for a disparate group of people linked together without their knowledge. Your family and friends would not be part of your karass. You wouldn't choose its membership, and you may never know who is in it or what its purpose is.