Thanks for the answers everyone. It sounds like there's not a consensus as there doesn't seem to be a generally accepted definition of "HVC" and it's not clear whether "HVC" is synonymous with "360". I was specifically asking about the term "HVC", not "360", as I'm under the impression they are two different things. My understanding is that 360 is an actual, unpublished level in the SkyMiles program for selected Delta customers, rather like Marriott Platinum Premier. I was trying to figure out if HVC was formally segregated by Delta in some way, even if not organized into the SkyMiles program.