Wiktionary
n. A group of two or more people who imagine or are manipulated to believe they share a connection based on some circumstance of little or no real significance.
Wikipedia
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 actually meaningless.
Granfalloon was a science fiction fanzine published by Linda Bushyager. It was nominated for the Hugo Award for Best Fanzine in 1972, losing to Locus; and 1973 (losing to Energumen). The first issue was published in 1966 in Pittsburgh, Pennsylvania. Suzanne Tompkins was co-editor for the first six issues. Twenty issues of Granfalloon were released, the last one in July 1976.
Contributors included Piers Anthony, Alicia Austin, Bill Bowers, Ron Bushyager, Grant Canfield, Don D'Ammassa, Steve Fabian, Alexis Gilliland, Mike Glicksohn, Terry Jeeves, Arnie Katz, Tim Kirk, Damon Knight, Frank Lunney, Sandra Miesel, Ron Miller, Andrew J. Offutt, Andrew I. Porter, Bill Rotsler, Robert Silverberg, Darrell Schweitzer, Mae Strelkov, Bob Tucker, Harry Warner, Jr., Ted White, Susan Wood and Roger Zelazny.
Suzanne Tompkins went on to publish the fanzine The Spanish Inquisition in the 1970s.
Bushyager also published the fanzine Kardass in the 1970s.