We deal a lot with equipotential planes in the IT field. It can be as simple as copper mesh or bonded rebar in the slab; in IT centers, it's common to have the (metal) false floor bonded to act as an equipotential plane. (Also helps dissipate harmonics-the capacitance of an equipotential plane to ground tends to clear higher frequencies extremely well.) But there really is no one standard industry definition- it's simple a plane at equal electrical potential. Conductive matting is another means- ask anyone who deals with explosives in a workshop setting, for instance, and they can tell you exactly what you need to do to completely eliminate shock hazards.
With no set definition, in the end, it's going to come down to an AHJ ruling.
