The term "limp-sissy" is related to a specific fetish or kink in the BDSM/kink community. Here's what it means:
"Limp" refers to the act of rendering one's limbs temporarily unable to move, often by using ropes or other bindings. This can be a form of submission or domination play in BDSM scenes. "Sissy," on the other hand, is a term that has been adopted by the kink community and refers to a submissive role taken by a male partner. It's often associated with humiliation or degradation play, where the sissy may be dressed up in feminine clothing or made to perform traditionally feminine tasks as part of their submission.
So, when you see "limp-sissy" in a porn video tag, it suggests that the scene involves both elements: the male character is submissive and limited in movement due to being tied up or otherwise restrained. This can result in scenes that involve humiliation, forced feminization, or simply a power dynamic between the dominant and submissive characters.