Refers to an emperor, especially of historical empires such as China or Rome, or in a general monarchical context. For the Emperor of Japan, 天皇 (てんのう) is the specific term.
Qin Shi Huang, the First Emperor, unified China.
Do you know the names of some Roman emperors?
He became the emperor of Rome.
He ascended to the throne as emperor at a young age.
The emperor of the Qing dynasty lived in Beijing.
After the rebellion, he declared himself emperor.