Bareback: This term in the context of porn videos refers to unprotected or condom-less sex. In other words, it means that the actors are having intercourse without any protection.
Shemale: This term is used to describe a person with male genitals but feminine characteristics or traits. It is often used in the transgender community and within the porn industry as a descriptor for performers who fall under this category. In the context of a porn video tag, "shemale" indicates that the scene features a performer or performers who identify as shemale, typically engaging in sexual acts with one or more partners.
So, "bareback-shemale" would mean a porn video featuring unprotected sex involving at least one shemale performer.