The term "sissy-m2f" is a combination of two concepts:
1. Sissy: This refers to a submissive male or a man who is submissive in nature, usually engaged in feminizing activities as part of their roleplay or kink. It can also refer to a man who is humiliated or degraded by being treated like a woman or made to perform traditionally female tasks.
2. M2F: This stands for "male-to-female," which is often used in the context of transgender individuals undergoing gender transition from male to female. In this case, it could be interpreted as a man who is transitioning or roleplaying as a woman.
So, the tag "sissy-m2f" refers to a porn video that features a submissive male or a man who is engaging in feminizing activities while transitioning or roleplaying as a female. This content is intended for an adult audience with specific interests in this type of fetish play and gender exploration.