I believe it is a state of mind and an approach to evaluating hi-fi systems
I associate the term negatively with hi-fi made by Linn or Naim
If you want flat earth only Linn or Naim will do.
alfie
Main System: Denon DP-6000 VPI Base/Fidelity Research FR64s/Ortofon SPU Royal GM MKII/Shelter 901/Auditorium 23 SUT/Pure Sound P10/SB Touch or Audio Note CDT & M2Tech Young Dac/BL Audio LP-1/New Audio Frontiers KT66 Legend/Living Voice OBX.
2nd System: PC/Foobar/E-MU 0404 pci (Modded)/AVI ADM9/Rel Strata II subs.