This porn video tag has two parts: "brunette" and "mtf".
1. "Brunette": In the context of adult content, this term refers to a person with brown hair or someone who is typically perceived as having brown hair. It can also be used as an adjective to describe any scene involving performers with brown hair.
2. "MTF" stands for "Male-to-Female". In adult content, this term refers to transgender performers who were assigned male at birth but identify and express themselves as female. MTF performers may undergo hormone therapy and other medical or surgical procedures to transition from male to female.
So, the tag "brunette-mtf" describes a porn video featuring a brunette transgender woman (female assigned at birth, but identifies and expresses herself as a man) who is typically involved in sexual activity with one or more partners.