The porn video tag "pretty-tgirl" refers to a transgender woman (Transgender Girl) who is considered attractive or aesthetically pleasing. In this context, "tgirl" is a term used to describe a transgender woman, and the addition of "pretty" emphasizes her beauty or physical attractiveness. This tag would be applied to a video featuring such an individual, potentially for the purpose of highlighting her visual appeal or as part of a search filter for users interested in transgender content.