Original: The Western Roman Empire refers to the western half of the Roman Empire, from its division by Diocletian in 285; the other half of the Roman Empire was the Eastern Roman Empire, today widely known as the Byzantine Empire.
Simplified: The Western Roman Empire was the western half of the Roman Empire, from its division by Diocletian in 286; the other half of the Roman Empire became known as the Eastern Roman Empire, today widely known as the Byzantine Empire.