"Rub-down" is a term used in the context of adult content, specifically in relation to massages and body rubs. In the context of a porn video tag, it typically means a scene involving sensual or erotic massage sessions between two or more people. This may involve different techniques such as stroking, kneading, and applying lotion or oil on various parts of the body. It can also indicate a more intimate scenario where sexual activities progress from the rub-down. Note that this term is not specific to English language, it's commonly used in adult content across several languages.