AV (anal intercourse, English "A-Levels") refers to anal sexual intercourse. Offered by some sex workers as an optional service, usually at an additional cost and always with a condom and lubricant. Preparation (hygiene, slow warm-up) is a prerequisite - professionals take their time.
Risks: Micro-injuries significantly increase the risk of STI transmission (especially HIV, hepatitis C). Changing condoms between anal and vaginal/oral is mandatory. If there is pain or bleeding: stop immediately.