Sissy dress-up is a term used in the context of BDSM and cross-dressing. In this type of porn video, one or more participants engage in dressing up in feminine clothing as part of their role play or submission to another participant. The term "sissy" often refers to the person who is being dressed up and may be involved in a humiliation or femdom aspect of the scene.
In these videos, you can expect to see participants dressing up in various female outfits such as dresses, high heels, lingerie, wigs, makeup, etc., often in a playful, submissive manner. The focus is on transforming the participant into a feminine appearance for the purpose of entertainment or role-playing. This tag typically appeals to those who enjoy gender role reversal and humiliation play within their adult entertainment.