"Pup" in the context of a porn video tag typically refers to a person dressed up in pet play or furry role-play attire, often wearing a dog mask and other related accessories. The term is derived from the animal's appearance and behavior, and can be associated with submission and dominance dynamics in BDSM play. The use of "pup" is primarily a form of fantasy and cosplay within the kink community and should not be confused with any form of animal abuse or harm.