Euthanasia is the process of having someone assist another with suicide. Although some cultures, such as Humans, consider the practice immoral, others, such as Vulcans, consider euthanasia of the elderly a normal practice.
In Spock's youth, the decision was made to euthanize his beloved pet sehlat I-Chaya when he was mortally wounded, rather than have an extended life in agony. This was a critical turning point in the young half-Vulcan's life. (TAS: "Yesteryear")
In the aftermath of Earth's Third World War, Colonel Green infamously euthanized hundreds of thousands of Humans who were suffering the effects of radiation poisoning. (ENT: "Terra Prime")
Klingons who have suffered an injury or wound that precludes their further service to the Empire may euthanasize themeselves by performing ritual suicide in a ceremony known as the Hegh'bat. (TNG: "Ethics")
References
- VOY:
- "Phage"
- "Emanations"
- "Coda"