Do not resuscitate

Wikipedia

Do Not Resuscitate (DNR), also known as no code or allow natural death, is a legal order, written or oral depending on country, indicating that a person does not want to receive cardiopulmonary resuscitation (CPR) if that person's heart stops beating.

England and Wales

In England and Wales, CPR is presumed in the event of a cardiac arrest unless a do not resuscitate order is in place. If they have capacity as defined under the Mental Capacity Act 2005 the patient may decline resuscitation, however any discussion is not in reference to consent to resuscitation and instead should be an explanation. Patients may also specify their wishes and/or devolve their decision-making to a proxy using an advance directive, which are commonly referred to as 'Living Wills'. Patients and relatives cannot demand treatment (including CPR) which the doctor believes is futile and in this situation, it is their doctor's duty to act in their 'best interest', whether that means continuing or discontinuing treatment, using their clinical judgment. If the patient lacks capacity, relatives will often be asked for their opinion out of respect.

More straightforward than its scary title implies.