This porn video tag, "big-butt-milf," refers to a specific genre or theme within adult content.
"Big butt" is a popular term used in the adult industry to describe a woman with an ample, well-shaped derriere. This is often considered visually appealing and sexually attractive.
"Milf" stands for "Mother I'd Like To Fuck." It describes a sexually attractive woman who is usually of a certain age (typically 30 years old or above), often with children, and is desired by younger men. The term implies that the woman possesses a combination of maturity, experience, and physical attractiveness.
So, when you see "big-butt-milf," it signifies an adult video featuring a sexually attractive older woman (typically a mother) with a large, well-shaped derriere who may be involved in scenes that cater to the fantasies of younger men. Remember, this is intended for an adult audience familiar with pornography and its terminology.