Final answer:
The term 'tetrarchy' refers to the rule by four emperors introduced by the Roman Emperor Diocletian to stabilize the Roman Empire. It consisted of two senior emperors, known as Augustus, and two junior emperors, known as Caesar.
Step-by-step explanation:
The term 'tetrarchy' was introduced by the Roman Emperor Diocletian and it means rule by four emperors. Diocletian established the tetrarchy as a way to stabilize the Roman Empire during the Crisis of the Third Century. The tetrarchy consisted of two senior emperors, known as Augustus, and two junior emperors, known as Caesar, who were intended to succeed the senior emperors upon stepping down.