disneysteve,
I always thought the definition was finished above ground living space, but it seems the finished basement is sometimes added in the calculation.
Here is a link to About.com
How to Measure and Calculate Residential Square Footage (About.com)
I go by what the County has listed because I am not sure about the basement. For us, the county has:
Above Grade Living Area Total Sq. Ft 1,620
It has a separate listing (as attached structures) for a porch 120 sq ft and attached garage 672 sq ft.
The co. website only says there
is a basement--no sq footage listed. (It is a finished basement with an exterior entrance).
Maybe the rules vary from county to county?