In fetish circles, the "FMG" acronym is supposed to mean "Female Muscle Growth"--which ranges from active muscle growth on ladies to all out amazonian giantesses--but since it's not really clarified, it could really be anything...
We all would. Then again, it might be just my heavily biased perception by my pet peeve of people who spew things they're into assuming eveyone else will know what they're refering to.