Font sizes for WCAG2.0 AAA

Anyone know what the WCAG2.0 definition of 'Normal' and 'Large' fonts are, as they relate to the AA and AAA levels?

I've googled and read the WCAG site and docs but unless I'm being really stupid (wouldn't rule it out) I just can't find it.

Ideally I'm looking for something along the lines of "18pt or larger is defined as large for WCAG guidelines" or something equivalent.