This porn video tag, "ftm-pee," stands for Female-to-Male (FTM) transgender individual engaged in Pee Play.
In the context of pornography, FTM refers to a person assigned female at birth who is in the process or has transitioned towards masculinity, either physically, mentally or both. Peeplay (also known as watersports) refers to activities involving the excretion of urine in an erotic context.
So, this tag describes a porn video featuring a FTM individual engaging in pee play, often for sexual pleasure and exploration of their identity. It is important to note that such activities should be consensual and safe for all involved parties.