Tom Forsyth is a former Valve and Oculus developer (and member of this forum). This is an interesting article on Inter Ocular Distance (between eyeball centres), Inter Pupillary Distance (between pupil centres), Inter Axial Distance (between lens centres) and Inter Camera Distance (between cameras in renderer).
(Note: Tom made up the last two terms because there's no convention for them)
Long story short: IOD is what we should be measuring on people. IPD changes based on what you look at (your pupils converge or diverge based on distance). IAD is what the slider on the Rift CV1 / Quest does and ICD is what the renderer is using.