Yea, just kinda depends on who you talk to. Some people say over, some say under.
For instance, when a crank gets .010" ground off it's journals, you'd say "well, it's a 10 under crank". Then you would go look for .010" under bearings, since the crank is .010" under.
There is a specific range of oil clearance that engineers design into bearings (usually measured in tenths of an inch) which is why you'll only find certain size bearings, and the crank should be ground accordingly.
Does that make sense? It's kinda weird how I write stuff sometimes.