m/f is an abbreviation used in spanking art to signify an artwork or story that features a minor male spanker and a minor female spankee. In other words, a boy spanking a girl. It could be, for example, a boy spanking his playmate, a girl from his school, his sister, or his cousin.
In the case where a boy will play "house" or "school" with girls, the boy may take the role of a daddy, teacher or principal and spank his "daughter" or "schoolgirl" for roleplayed misbehavior or poor work. Although this is roleplayed M/f, in reality it is m/f.
m/f is girl spanking art.
 See also