Actually I prefer the more technical term of cultivar, which is short for "cultvated variety". Sometimes you will see it abreviated as cv.
First place I ever saw it used was in some of my bamboo books and catalogs to describe the varieties of bamboo that are divergent in appearance from the standard species it is derived from. I thought this was pretty much what we are doing with the corn snakes, and certain is an apt description of what we are doing.
I believe it can refer to anything we are willing to give a name to that is used as an identifying label. Whether it be a genetic trait, locality specific variance, or just something that is undecided, yet definitely identifiable in appearance one way or another.
I don't think the term will catch on in the herp world, but I tend to use it, nonetheless.
"Morph" got tainted in my brain by computer programs and such that implied something that can change from one moment to the next. Such as morphing an image via animation, or some sort of comic book characters that could change shape and appearance at will.