What is the Hijra (not Hajj!) ?

The Hijra was when the prophet Muhammad along with Abu-Bakr migrated from Makkah to Maddinah. The Hijra became the start of the Islamic calendar after the passing of the prophet Muhammad under the caliph leader Umar Ibn Al-Khatabb

The Hegira is the journey or migration of Muhammad (the Islamic prophet) and his followers from Mecca to Yathrib in 622. After getting a warning from a group he and his followers surreptitiously left his residence in Mecca to migrate to Yathrib which was 320 km north of Mecca. In his migration, he was followed by Abu Bakr who later became one of the Caliphs.