What is Surrogate Decision-maker?

Legal Definition
A surrogate decision maker, also known as a health care proxy or as agents, are advocates for incompetent patients. If a patient is unable to make decisions or decide for themselves about personal health care, someone else must provide direction in decision-making, as the surrogate decision-maker. If there is a durable power of attorney for health care, the agent appointed by that document is authorized to make health care decisions within the scope of authority granted by the document. If people have court-appointed guardians with authority to makes health caring decisions, the guardian is the authorized surrogate.
-- Wikipedia