A martyr is one who gives his life for Christ, physically dying as a witness to the faith. Martyr itself comes from the Greek μαρτυρος, which means "witness." By traditional liturgical ranking, the martyrs are first among the saints.
Tertullian once said that "the blood of the martyrs is the seed of the Church," and the Body of Christ continually witnesses to this reality. Where the persecution of the Orthodox faith becomes great enough that Christians are killed for their faith, history typically records a resurgence of faith and piety among the people of that region.