The tag "cm3d2-anal" refers to a specific porn video featuring the characters from the hentai series "CM3D2" engaging in anal sex. CM3D2 is an abbreviation for "Crossings of the 3rd Dimension - Mozaik," which is a Japanese adult visual novel and anime series. The term "anal" refers to the type of sexual activity being depicted in this video, specifically involving anal intercourse. Therefore, this tag indicates that the porn video contains content from the CM3D2 universe focused on anal scenes.