Consensual

In common speech, consent occurs when one person voluntarily agrees to the proposal or desires of another. The concept of consent has been operationalized in several major contexts, including in law, medicine and sexual relationships. Types of consent include implied consent, expressed consent, informed consent and unanimous consent. Consent as understood in legal contexts may differ from the everyday meaning. For example, a person with a mental disorder, one with a low mental age or one under the legal age of sexual consent may willingly engage in a sexual act, but that consent is not valid in a legal context.

Consent can be either expressed or implied. For example, participation in a contact sport usually implies consent to a degree of contact with other participants, implicitly agreed and often defined by the rules of the sport. Another specific example is where a boxer cannot complain of being punched on the nose by an opponent; implied consent will be valid where the violence is ordinarily and reasonably to be contemplated as incidental to the sport in question. Express consent exists when there is oral or written agreement, particularly in a contract. For example, businesses may require that persons sign a waiver (called a liability waiver) acknowledging and accepting the hazards of an activity. This proves express consent, and prevents the person from filing a tort lawsuit for unauthorised actions.

In English law, the principle of volenti non fit injuria applies not only to participants in sport, but also to spectators and to any others who willingly engage in activities where there is a risk of injury. Consent has also been used as a defense in cases involving accidental deaths during sex, which occur during sexual bondage. Time (May 23, 1988) referred to this latter example, as the "rough-sex defense". It is not effective in English law in cases of serious injury or death.

...
Wikipedia