F2M stands for "Female to Male," which refers to content involving a transgender man or someone who identifies as male but was assigned female at birth. Masturbation is the act of touching one's own genitals for sexual pleasure, typically leading to orgasm. So, "f2m-masturbation" tag indicates a porn video featuring a transgender man (or someone with a similar identity) engaging in self-pleasure by masturbating. This content is specifically geared towards adult audiences who are interested in or have experience with this niche category of pornography.