Definition from Nolo’s Plain-English Law Dictionary
An agreement to do something or to allow something to happen, made with complete knowledge of all relevant facts, such as the risks involved or any available alternatives. For example, a patient may give informed consent to medical treatment only after the health care professional has disclosed all possible risks involved in accepting or rejecting the treatment. A health care provider or facility may be held responsible for an injury caused by an undisclosed risk. In another context, a person accused of committing a crime cannot give up his constitutional rights -- for example, to remain silent or to talk with an attorney -- unless and until he has been informed of those rights, usually via the well-known Miranda warnings.