Well I guess I was wrong. I defer to Sheldon Brown:

Granny Gear

Slang term for the smallest chainwheel on a triple crank set.

Note that this term is not a general term for the lowest gear of a bicycle, but specifically refers to just the smallest chainwheel on a crankset with more than two chainwheels.

http://www.sheldonbrown.com/gloss_g.html