Longman Dictionary of Contemporary English
The Collaborative International Dictionary
living will \liv"ing will\ A document signed by an individual expressing his/her desire that, in the event of an illness from which there is no reasonable expectation of recovery, aggressive or extraordinary measures to prolong life, such as resuscitation and life-support equipment, should not be used.
Wiktionary
n. (context legal English) A document, made by a person when still legally fit to do so, expressing his desire to be allowed to die instead of being kept alive by artificial means, in the event of being severely disabled or suffering from a terminal illness.
WordNet
n. a document written by someone still legally capable requesting that they should be allowed to die if subsequently severely disabled or suffering terminal illness; "after he discovered he had AIDS he drew up a living will"
Wikipedia
Living Will... is an American comedy film starring Ryan Dunn, Gerard Haitz and April Scott.