Which of the following is a legal document providing guidance on a person's health care preferences?

An advance directive is indeed a legal document that outlines an individual's health care preferences in the event that they become unable to communicate their wishes due to illness or incapacitation. This document plays a crucial role in ensuring that medical decisions align with the person's values and desires, as it can specify different types of medical care one may or may not want.

While other terms such as living will and healthcare directive closely relate to the concept of advance directives, they can sometimes be more specific or used interchangeably in different jurisdictions. For instance, a living will typically focuses on specific medical treatment preferences, particularly regarding end-of-life care, while a healthcare directive may also encompass other healthcare decisions but doesn't necessarily carry the same legal implications in all areas.

Power of attorney differs as it primarily grants someone else the authority to make decisions on the person's behalf, but it is not directly a document focusing on the healthcare preferences of the individual itself. Thus, the advance directive remains the most comprehensive term for this type of legal guidance concerning an individual's health care preferences.