Edge play is dangerous; do not try this at home!
CNC, or Consensual Non-Consent, is an advanced form of relationship Negotiations in Power exchange dynamics that indicate that the S-type has voluntarily given up the right to make decisions in one or more areas of their life to the D-type, either permanently or temporarily. In cases where this is in all areas the appropriate term is TPE and this term is most often used in when describing M/s relationships.
Consensual Non-Consent indicates that the s-type will give authority regarding these negotiated areas to the d-type even in instances where the outcome of that decision may cause them discomfort.
Many believe that because the s-type may experience discomfort at the whim of the d-type without any recourse that the d-type has too much potential for abuse for this to be practiced in accordance with SSC. Proponents of this style of relationships indicate that these relationship paths are sustainable, mutually beneficial, happy and rewarding, to include a lack of Abuse as Consent is always maintained.
In the cases of TPE the adult entered into a Contract (verbal or written) of informed consent and has exercised their rights to give up their rights to another and thus consented as part of the contract. Further, no legal court in the modern world will uphold these contracts, and thus maintenance of the contract requires the continued consent of the s-type throughout the contract, however, it is important to note that while legal systems may not enforce these contracts, many areas will not accept consent as a defense for what they define as abuse. Be sure to understand the applicable laws of the region you live in regarding BDSM.