As far as the term "American" Saxony, I have only seen that term used a couple of places. Holderread uses it in his book to describe common colors that are like Saxony, but not exactly. He mentions a couple of examples one of which I'm almost sure was for ducks that appear to be Saxony color, but carry Buff dilution and are sometimes mismarked as true Saxony. I think he lists at least one other example, but I don't remember what it is.
Goosedragon is right though (as usual, LOL), Saxony is both a color and a breed. Genetically, it is basically light phase wild type with double blue dilution (Holderread himself though has used at least two different genotypes for Saxony over the years, but wild type plus li/li, Bl/Bl is the currently accepted genotype). Anyway, it is a rather easy color to breed for and has been bred in numerous types of ducks. I am working on developing a bantam Saxony which I may start selling next year and also have Saxony Runners (most of them bred by Holderreads). It is a beautiful color, probably my favorite! The Saxony breed is awesome too.