F/F
F/F is an abbreviation used in spanking art to signify an artwork or story that features an adult female spanker and an adult female spankee.
F/F spanking drawing by Funbun.
It could be, for example, a historic mistress/maid scene. Besides spanking for discipline, adult spankings in art and literature are also often erotic spankings in sexual scenes. In the case of F/F, these might be lesbian.
F/F is woman spanking art.