"Bonus" in this context refers to a special feature or additional content, often included as a bonus for viewers. In the case of porn videos, it may indicate a scene or video that is not part of the main storyline but offers extra pleasure.
"Hole-ftm" stands for "Female-to-Male." This term refers to transgender or transsexual individuals who were assigned female at birth but identify and express themselves as male. In a porn context, it often signifies scenes featuring such performers engaging in sexual activities with other partners.
So, the tag "bonus-hole-ftm" means a bonus scene or video involving a Female-to-Male transgender performer participating in sexual activities.