The porn video tag "3d-mmd-sex" refers to a specific genre of adult content created using 3D modeling and MMD (Miku Miku Dance) software.
3D models are digital representations of objects or characters in a virtual three-dimensional space. In this context, "3d" indicates that the video features 3D animated graphics.
MMD is a freeware motion capture software developed by Yu Peng, a Japanese programmer and animator. It allows users to create and animate 3D models using pre-made character models or their own custom characters. The "mmd" in the tag signifies that the video was created using this particular software.
Lastly, "sex" refers to the explicit adult nature of the content, which typically includes sexual acts or nudity involving the 3D animated characters.
So, the tag "3d-mmd-sex" describes a specific category of pornographic video where the characters are 3D models created and animated using MMD software, containing explicit sexual content.