I get how Hoosiers are a granfalloon (the borders of the state of Indiana being essentially arbitrary), but how are groups defined by a shared philosophy and b

I get how Hoosiers are a granfalloon (the borders of the state of Indiana being essentially arbitrary), but how are groups defined by a shared philosophy and belief system like the Communist party a granfalloon? Like, what are some examples of groups that everyone would agree are definitely a “karass” rather than a “granfalloon”?