Euthanasia is best described as:

Euthanasia is best described as assisting patients to end their lives due to suffering. This definition captures the essence of euthanasia, which involves a deliberate action taken to alleviate unbearable suffering, typically in individuals with terminal or debilitating conditions. It reflects the ethical and compassionate decision-making process that some health care providers and families may consider when faced with severe pain and a poor quality of life due to illness.

The other options misrepresent the concept of euthanasia. For instance, prolonging life for terminal patients refers to efforts aimed at extending lifespan, often through medical interventions. Reviving individuals is related to resuscitative efforts rather than ending life. Finally, administering extreme pain relief medication might be a component of palliative care, which focuses on comfort, but it does not equate to euthanasia, which is explicitly aimed at ending life. Thus, the chosen answer accurately encapsulates the complex ethical considerations surrounding the practice of euthanasia.