Hard cheeses generally have a thick rind (though if you don't purchase
full wheels, the rind may have been removed by the time it gets to you)
and are often waxed, oiled, or clothbound. The hardness of a cheese
is largely due to how much whey is lost from the curd before it's put
into a mould. Reducing the moisture in the curd lengthens the
fermentation process, producing more rounded flavor. Most hard cheeses
require at least a few weeks to mature (in caves or other cool, humid
places); the longer a cheese ages, the stronger its flavor.
Common hard cheeses include Parmigiano-Reggiano, Cheddar,
Manchego, and Gruyère.
The texture of hard cheeses make them ideal for grating, and the
concentration of flavor with minimal moisture makes them good candidates
tells me that 'hard cheese' is British
slang for tough luck
. It's been in use since at least the late 1800s.