It's been about 40 years since I've heard anyone use the term, but music students at Friends University (who taught me a lot of my music theory while the big guys were chasing the grrrls at the social meetings) did mention and discuss it some, so it's not a figment of NPR delusions.

I'd assume that it was one of those theoretical notions associated with older and/or "church" music forms, as it didn't seem known to the SPEB activists I knew then; but I can't really offer anything very useful other than it is (or once was) a real idea.

John