This porn video tag refers to the fact that the video is available for viewing without any costs. In other words, you can watch it for free. As a content editor who writes clear descriptions of porn video tags, I'd describe this as:
Free Porn Video: Indicates that this adult movie or clip can be viewed at no cost by viewers. Note: This tag is intended to inform potential viewers about the accessibility of the content and not to imply or encourage any specific behavior or actions