The word 'variant' has a couple of meanings especially insofar as fly tying:
It is used as an adjective to describe a pattern that deviates from the norm with just a slight difference, i.e. you might use a rib of silver tinsel instead of gold, or cree hackle instead of grizzly and brown. It is also used as a noun when it describes the name of a specific pattern, i.e. Gray Fox Variant, or Cream Variant.