Short answers, pulled from the story.
The Greek word mártys originally described someone who spoke from personal observation. Aristotle and Plato used this term for observations and ethical judgments that could not be empirically observed before early Christians adopted it to describe witnesses of Christ's public life.
The period before Constantine I became known as the Age of Martyrs during the first three centuries of the Christian church. This era involved periods of persecution at the hands of Roman authorities where local officials acted on an intermittent basis while empire-wide persecutions were directed from Rome.
Stephen stands as the first martyr reported in the New Testament. He was accused of blasphemy and stoned by the Sanhedrin under Levitical law toward the end of the first century.
The Center for the Study of Global Christianity at Gordon, Conwell Theological Seminary previously estimated that 100,000 Christians die annually for their faith. Todd Johnson later stated his center abandoned this statistic after discovering most deaths occurred during the Civil War in the Democratic Republic of Congo.
Tertullian, a second-century ecclesiastical writer, stated that the blood of martyrs is the seed of the Church. This phrase implied that a martyr's willing sacrifice leads to the conversion of others.