Not being a Canon guy I am not sure what the game is. But it means the ISO setting that is 1/3 of a stop below what is labelled as ISO 3200 in-camera.
Thanks for the RD chart.
The game, as I understand it, is that for Canon 5D series (and other Canons...not some 1D's) they only really have true ISOs at full stops.
The 1/3 stops are "fake". That is, if you set 160 ISO, it is really 200 ISO, but metering done as 160...therefore 1/3 stop overexposed...as in slight ETTR. Therefore the shadows are slightly better.
For jpeg OOC, the RAW is pulled back 1/3 in the OOC post processing. For 1/3 stop ISOs over the full stops, the image is pushed up in post.
I, personally, just set my camera to full stop ISO. Since I shoot RAW only, I want to control whatever "ETTR" I am doing.