"Sissy in heat" is a term used in the context of BDSM and humiliation roleplay in porn videos. It typically refers to a submissive male character, often dressed as a woman or wearing feminine attire, who is being treated as if they are in heat, like an animal.
This tag suggests that the video may involve the sissy being teased, tormented, or sexually used by a dominant character due to their perceived "heat" or heightened sexual desire. This could include elements of humiliation, cross-dressing, forced feminization, and other BDSM practices. The focus is on degradation and the objectification of the submissive male character for the pleasure and dominance of the dominant partner.