In Jainism, the vow of voluntary fasting unto death at the end of life is called:

"Sallekhana" (also called "Santhara" or "Samadhi-marana") is the Jain practice of voluntarily and gradually giving up food and water at the end of life.

About Sallekhana:

• It is undertaken when a person feels that death is near, because of old age, incurable illness or severe famine, and when they can no longer follow their religious duties.
• The person gradually reduces food and drink, and spends time in meditation and prayer, with a calm mind, free from fear, desire and anger.
• It requires the permission of a religious teacher.
• It is regarded by Jains as a peaceful and spiritual way to face death, which helps the soul shed karma.
• Jains do not consider it suicide, because it is not done out of despair or emotion, but as a religious practice with full awareness and detachment.

History:

• Inscriptions at Shravanabelagola and other places in Karnataka record many cases of Sallekhana by monks, nuns and lay people over many centuries.
• According to Jain tradition, a famous ancient emperor, who had become a Jain monk, ended his life through this practice at Shravanabelagola.

Legal debate:

• In August 2015, the Rajasthan High Court declared Santhara illegal, treating it as equivalent to suicide.
• The Jain community protested, and the Supreme Court stayed the High Court's order soon after, so the practice continues.

Other Jain practices:

• "Kayotsarga": a standing posture of meditation, with the body still and arms hanging down.
• "Pratikramana": a ritual of repentance for wrongdoings.
• "Paryushana": an annual festival of fasting, forgiveness and reflection, ending with "Samvatsari", when Jains ask for forgiveness with the words "Michhami Dukkadam".
• "Das Lakshana": the Digambara form of Paryushana.

Why not the other options?

• ✗Kayotsarga is a meditation posture.
• ✗Pratikramana is a ritual of repentance.
• ✗Paryushana is an annual festival.