Climate Zones are zones created by the USDA that segregate the US into
areas with common temperature extremes. The borders of the zones run
roughly east/west and are numbered *I think* with the lowest #s
(coldest temps) in the North. There are about 10 zones. Most of the seed
packets sold in the US have a tiny reproduction of the official USDA zone
map on the back and give you planting dates depending on which zone you
live in.
As I child of the digital age I naturally went to http://www.usda.gov
but had no luck finding a climate zone map there. I didn't search the
whole site though and I'm sure there's one somewhere at one of the .gov
domains.
Hope this helps,
Phil