Consent occurs when one person voluntarily agrees to the proposal or desires of another. It is a term of common speech, but may have more specific definitions in such fields as the law, medicine, research, and sexual relationships. Types of consent include implied consent, expressed consent, informed consent and unanimous consent. Consent as understood in specific contexts may differ from its everyday meaning. For example, a person with a mental disorder, a low mental age, or under the legal age of sexual consent may willingly engage in a sexual act that still fails to meet the legal threshold for consent as defined by applicable law. UN agencies and initiatives in sex education programs believe that teaching the topic of consent as part of a comprehensive sexuality education is beneficial. 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.