"FTM" in this context stands for "Female to Male," referring to a transgender man or person assigned female at birth who is transitioning to male. In the context of a porn video, it suggests that the scene involves a trans man with a penis and testicles, typically having sex with another partner.
"Anal" is short for anal sex, which means the sexual activity in this scene will involve penetration of the rectum. This can include various forms of penetrative sex like penetration using a penis, dildo, butt plug, or fingers.
So, the tag "ftm-anal" refers to a porn video that features anal sex with a trans man (female to male) as one of the participants