This tag is a combination of four terms that describe the content of the porn video:
1. "Solo": This indicates that there is only one performer in the scene, without any additional participants.
2. "Tranny": This refers to a transgender or transsexual performer, often with male-to-female (MTF) transition.
3. "Jerking": Also known as masturbation, this term describes the act of pleasuring oneself in the video.
So, the tag "solo-tranny-jerking" refers to a porn video featuring a transgender or transsexual performer who is masturbating by themselves without any other participants involved.