Teen: The person involved in the scene is a young adult, typically under 18 or appearing to be. This implies that the participant is experiencing sexual activities for the first time or at an early age.
Shemale: Refers to a performer who has male genitalia and female characteristics. Typically, this involves hormone treatments and/or surgeries that result in breast development and sometimes, a more feminine appearance.
Solo: The scene features one person engaging in self-pleasuring or masturbation activities, without the involvement of another performer.
In summary, "teen-shemale-solo" is a tag for a video featuring a young adult with male genitalia and female characteristics, who engages in solo masturbation activity. This content is explicitly intended for an adult audience familiar with porn videos.