A Living Will is a statement by you to the world that if your condition is determined to be terminal and incurable you do not want your life prolonged by extraordinary means such as artificial nutrition or hydration, or other life sustaining procedures.
This document directs and authorizes the physician to withhold and discontinue extraordinary means. The procedures and treatments to be withheld and withdrawn include surgery, antibiotics, CPR, and artificially administered feeding and fluids. The treatment is limited to measures which comfort and relieve pain, even if such measures will shorten your life.
Thinking about our death is difficult and depressing. But, putting in place now the means for your wishes to be respected is well worth it in the long run when it comes time for your family to refuse medical treatment on your behalf.