Consensual non-Consent refers to an agreement done prior to play, where both sides agree to act as though consent has been waived, and trust that the other person will not cross any hard limits. In consensual non-consent scenarios, the dominant will often have blanket permission to indulge in any activity that is allowed by negotiation, even without giving their partner any information about what they plan to do ahead of time. The use of safewords, and/or the red/yellow/green system is often the only way for the sub to end the scene. Aside from that, anything that happens will be considered consensual by both parties.
This arrangement requires tremendous trust between the partners and the utmost clarity on the limits.
Consensual non-consent can also refer to roleplaying rape scenarios, where the dom is encouraged to ignore normal cries to stop. Once again, the use of safewords is a must in these scenarios