That is shipments during a fiscal year. (In this case it's the FY ending March 21, 2009.) VGChartz has the highest calendar year being the DS in 2008 with 29.7m.
Of course, there is 9 months of overlap between those two time periods. There is also a lot of overlap between the current calendar year and the current FY. We might be having a very similar discussion around the end of March next year about highest FY of all time.
Ah, gotcha, so no system has ever sold 30 million in a calendar year before.
Gosh I so hope Switch does, just cos it'd be so insane to see. I'm expecting more in the 26-28 million range cos of supply limitations, but you never know.