What exactly does the term "Caesar" signify?

Question

Is Caesar the surname of the line of Roman Emperors, or is just the title they used?

Answer 1

Originally, there was Julius Caesar. A family name. He adopted his nephew Octavius, who became the first emperor (imperator). Octavius Augustus Caesar was followed by four relatives as emperors, members of the Caesar family: Tiberius, Gaius Caligula, Claudius, and Drusus Nero.

After the death of Nero, the Roman Senate voted all of the titles and powers of emperor to six more persons, and the Senate "adopted" them into the Caesar family: Galba, Otho, Vitellius, Vespasian, Titus, and Domitian.

After Domitian (d. 97 ce) followed the "Five Good Emperors." They did not take the family name of Caesar.

In 285 ce, Diocletian became sole emperor and divided the empire into four parts. Two parts were to be governed by emperors called Augustus. The two Augusti were to have two junior emperors called caesars. This lasted 20 years.

About the year 1080, in Constantinople, the time of the Byzantine empire, the title Caesar was intended to mean next in line for the throne. The emperor was now called basileus.

In modern times, the Emperor of Germany (1871-1918) was called Kaiser. ("Kaissar" was the pronunciation of "Caesar" by Romans in ancient times.)

Answer 2

It was the title they used in the tradition of the first emperor Augustus, who was the nephew of Julius.