The act of painlessly ending the lives of individuals who are suffering from an incurable disease or severe disability is called mercy killing, or

Euthanasia

Explanation:

Euthanasia is also another word for mercy killing. It is a death that is easy or death that is without pain. Euthanasia describes the act of putting an end to a person's life. This could be done at the request of the person who might be suffering from an incurable ailments or one who is in Great pains. It can be carried out through the use of lethal injections which would shut down the heart and brain in a few minutes.

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