What is "grey market non-US product" in terms of buying Canon lenses?

I'm looking at buying a telephoto lens for my new Canon SLR camera. One fo the offerings that is $40.00 cheaper for the same items suffixes the description with "gray market non-US product" I'm just trying to figure out what it means for both the product and the service of it.|||The product is fine, it's the real Canon product. Warranty is another issue - you get a cheaper price mainly because you're on your own. Gray market products are legal, it's just that they were not intended for the local market and are often not sold by authorized dealers.|||It means the lens was intended to be sold in another country and is not covered by a US warranty.