A granfalloon, in the fictional religion of Bokononism (created by Kurt Vonnegut in his 1963 novel Cat's Cradle), is defined as a "false karass". That is, it is a group of people who affect a shared identity or purpose, but whose mutual association is meaningless.
As quoted in And So It Goes: Kurt Vonnegut: A Life (2011) by Charles J. Shields, Vonnegut writes in his introduction to his book Wampeters, Foma and Granfalloons (1974) that a "granfalloon is a proud and meaningless collection of human beings"; Shields also comments that in the same book, Vonnegut later cites the demonym of 'Hoosiers' as "one of [Vonnegut's] favorite examples" of what the term embodies. Another example of a granfalloon given in Cat's Cradle is 'alumni of Cornell University'. Kurt Vonnegut himself was born in Indiana and attended Cornell University.