What term refers to the act of ending the life of an individual in great pain?

The term that refers to the act of ending the life of an individual who is experiencing great pain is euthanasia. Euthanasia is typically characterized by the intention to alleviate suffering, often in cases of terminal illness where an individual's quality of life has significantly diminished. It involves a healthcare professional administering a substance that causes death to relieve intractable pain or suffering.

While other options may sound similar or relate to similar concepts, euthanasia specifically denotes the process where medical intervention is actively used to end life as a compassionate response to unbearable suffering. This distinguishes it from assisted suicide, where an individual takes their own life with assistance or guidance from a medical professional, but does not involve direct action from the healthcare provider to end the patient's life. Palliative care focuses on providing relief from pain and other distressing symptoms without hastening death, promoting comfort rather than actively ending life. Mercy killing, while often used colloquially in a similar context as euthanasia, may not carry the same legal or medical definitions and can imply more ambiguous ethical considerations. Hence, euthanasia is the most precise term for the context given in the question.