A requirement limit is a BSDM term used to describe things dominants or submissives absolutely need when taking part in a BSDM scene. These are things that participants will refuse to do the scene without, and may include certain acts or even aftercare.
A requirement limit may also be known as a must limit.
More About Requirement Limit
Negotiating limits is a big part of BDSM and many of its practitioners' goal to engage in sex play that is always safe, sane and consensual. A requirement limit is the opposite of other types of limits that are set to prevent certain acts and sorts of play, and instead aims to lay out play that couples enjoy and consider essential for having a good time.
This sort of communication need not apply only to BDSM, though. Letting partners know what you want and what's essential to your pleasure should open the lines of communication and even improve your sex life.