Jay,
In the context of flies, the word 'variant' has 2 grammatical functions and has 2 meanings.
1) It can serve as an adjective as in "That fly has a slightly different wing". - var?i?ant adjective \ˈver-ē-ənt\ : different in some way from others of the same kind.
2) It can serve as a proper noun as in the name of a specific fly pattern as in The Gray Fox Variant, Cream Variant, Dun Variant.
Now, let's see someone define 'dun', lol.