There are many definitions and models of consent out there, but this is the one we prefer:

Affirmative Consent: “An informed, authentic and explicit agreement, freely given between two legal adults in a non-altered state of mind to allow a specific set of activities to happen during a specific time frame.”

Every word in that definition is important:

• Informed – You must know what you are agreeing to and the possible risks and implications you are exposing yourself to. Education and understanding are critical to consent. If you don’t understand the potential risks and implications of an activity, how can you authentically state that you accept those risks? Top or Bottom, you need to understand everything in the risk & safety section, because without that understanding, informed consent is not possible. Without knowledge, you are not informed.
• Authentic – Actively interested and willing to participate in the activities proposed. To be authentic, agreement must be informed and freely given. Some people like to use the phrase “enthusiastic consent”, because when someone is truly into something, that often comes across as enthusiasm, but we like the term “authentic” better because not everyone displays enthusiasm, even under conditions of great excitement. … And it is pretty common for a sub to be anything but enthusiastic if they are on their way to a punishment they know they have earned.
• Explicit – All people involved, having clear understanding of all the activities being proposed — everything on or off the table — all clearly state that they agree to take part in those activities. No assumptions. No implications. No innuendos.
• Freely given – Consent is only valid if it is freely given, with no coercion; be it physical, emotional, social, psychological, or chemical (drugs or alcohol).
• Legal adult – Any person who is not a legal adult in the jurisdiction in which an activity is taking place cannot legally consent to any sexual activity or activity related to sex.
• Non-altered state of mind – A person under the influence of any mind-altering influence or substance cannot consent to anything, even if they agree to it. A person who is asleep cannot consent.
• Specific set of activities – If someone consents to a chest harness scene, that is *not* consenting to a waist harness and certainly not to being groped or penetrated in any way. Consent to one type of sexual contact does not mean consent has been given for any other type of sexual contact. Do *not* include *any* activity that you did not specifically and clearly include in the negotiation *before* the scene.
• During a specific time frame – Just because someone consented to something yesterday does not mean you get to do that same thing again today, or ever.

If you have never seen the “Tea and Consent” video, treat yourself! ConsentIsEverything.com

The National Coalition for Sexual Freedom has much more on this.

Common Consent Models

There are several consent models out there. In the kink world, the two most popular are SSC and RACK.

SSC – Safe, Sane, Consensual

This was used for years, but it has a few issues: Who defines safe? Who defines sane?

RACK – Risk Aware Consensual Kink

This one recognizes that many things we do involve risk and that a critic could easily label them as “unsafe” or “not sane.”

This model places more responsibility on the individuals involved. You are entering into a situation in which you are aware of the potential risks and accept that what you are choosing to do may not necessarily be “safe” to some people.

This consent model is built upon the awareness and knowledge of all parties involved. Under RACK, one cannot ethically consent without knowing and understanding the risks involved in what they are doing. This is especially important in the context of rope, as Rope Bottoming can be quite dangerous, especially if a Bottom does not know the signs and symptoms that could indicate a problem that could lead to injury.