Double in the context of a porn video tag typically refers to scenes or content featuring two individuals engaging in sexual activities together. This can include various scenarios such as:
1. Two men (MM) - male-male sexual interaction
2. Two women (FF) - female-female sexual interaction
3. One man and one woman (MF) - mixed-gender sexual interaction
4. Multiple partners - group sex or threesome involving two men, two women, or a mix of both with the third participant.
Double can also refer to the presence of two penises, two vaginas, or other genitalia involved in the scene. It may indicate a more explicit or intimate exploration of sexual activities compared to single partner scenes.