One who voluntarily suffers death rather than deny his religion by words or deeds; such action is afforded special, institutionalized recognition in most major religions of the world. The term may also refer to anyone who sacrifices his life or something of great value for the sake of principle.
The universality of persecution throughout its history has engendered in Judaism an explicit ideal of martyrdom. It begins with Abraham, who according to legend was cast into a lime kiln and saved from the fire by divine grace. The tradition was continued by Isaac, who consented to be sacrificed by his father, and by Daniel, whose example compelled the popular imagination.
The original meaning of the Greek word martyr was "witness;" in this sense it is often used in the New Testament. Since the most striking witness that Christians could bear to their faith was to die rather than deny it, the word soon began to be used in reference to one who was not only a witness but specifically a witness unto death. This usage is present, at least implicitly, in Acts 22:20 and Revelation 2:13.
The Islamic designation shahid (Arabic: "witness") is equivalent to and in a sense derivative of the Judaeo-Christian concept of martyr. The full sense of "witness unto death" does not appear in the Quran but receives explicit treatment in the subsequent Hadith literature, in which it stated that martyrs, among the host of heaven, stand nearest the throne of God.
While distinctly lacking a history of persecution or of violent conflict with other faiths, Buddhism does recognize among its adherents a venerable class of martyrs. The Jataka (q.v.) commentary on the former lives of the Buddha is in a sense a martyrology of the bodhisattva ("buddha-to-be") and his disciples, recounting their continual self-sacrifice and repeated deaths. In Mahayana (Greater Vehicle) Buddhism, the decision by one destined to become a buddha in this or another life to postpone his own enlightenment to alleviate the suffering of others is regarded as martyrdom.
From the spiritual state of God-union (spiritual enlightenment, Nirvana, Samadhi, one's final surrender, At-Onement, etc., etc.) suicide and killing (for any reason) is the unlawful concept of the separate (from God) ego-I eccentric mentality.
Socrates rejects suicide, but drank hemlock as the fate for his physical body (but not his eternal spiritual self). Jesus also accepted the fate for his physical body knowing they could never kill or destroy his true spiritual nature.
The Holy War is the inner battle (same as the inner battle of Arjuna in the Bhagavad-Gita) of overcoming the limitations of the physical body and its self created physical psychological ego-I mentality. Meditation causes the apocalypse (destruction) of the outer self (lower mind) and the beginning of a new life. In Islam, this is the "final surrender" that is found in deep meditation that Mohammed (BPUH) discovered in the cave, and is his true teaching which is the same teaching from all true and loving teachers (i.e., Don't just worship God - as a separate being - but become god in a state of God-union). Only this is REAL GOD (i.e., There is "no God but God." (Actual attainment, not thinking or feeling - but the actual moment to moment actual experience of holy divine transfiguration as the foundation of one's new life as eternal spirit-mind.)