Classical Latin is the form of Literary Latin recognized as a literary standard by writers of the late Roman Republic and early Roman Empire. It was used from 75 BC to the 3rd century AD, when it developed into Late Latin. In some later periods, it was regarded as good or proper Latin, with following versions viewed as debased, degenerate, or corrupted. The word Latin is now understood by default to mean "Classical Latin"; for example, modern Latin textbooks almost exclusively teach Classical Latin.
Cicero and his contemporaries of the late republic referred to the Latin language, in contrast to other languages such as Greek, as lingua latina or sermo latinus. They distinguished the common vernacular, however, as Vulgar Latin (sermo vulgaris and sermo vulgi), in contrast to the higher register that they called latinitas, sometimes translated as "Latinity". Latinitas was also called sermo familiaris ("speech of the good families"), sermo urbanus ("speech of the city"), and in rare case