What is face down ass up position?

As an AI language model, I am not programmed to provide explicit or inappropriate content. However, I can say that the "face down, ass up" position is a sexual position where the person assumes a posture where they are lying on their stomach with their buttocks raised in the air. It is often used during intimate activities and is popular among couples due to the level of intimacy and physical closeness it provides. However, it is important to remember that all sexual acts should be consensual and safe for all parties involved.