What does the Hijra symbolize in Islam and what did it start?

It means "sacred" and marks the beginning of worshipping in mosques.
It means "prophesize" and marks the beginning of the sunnah tradition.
It means "divide" and marks the beginning of the Sunni-Shia split.
It means "migration" and marks the beginning of the muslim Era.
choose one

It means "migration" and marks the beginning of the Muslim Era.