Just out of curiosity, you studied Latin in the US? And have you read Cicero?
Since we are quoting Wikipedia:
"The concepts and vocabulary from which vulgare latinum descend were known in the classical period and are to be found amply represented in the unabridged Latin dictionary, starting in the late Roman republic. Marcus Tullius Cicero, a prolific writer, whose works have survived in large quantity, and who serves as a standard of Latin, and his contemporaries in addition to recognizing the lingua Latina also knew varieties of "speech" under the name sermo. Latin could be sermo Latinus, but in addition was a variety known as sermo vulgaris, sermo vulgi, sermo plebeius and sermo quotidianus. These modifiers inform post-classical readers that a conversational Latin existed, which was used by the masses (vulgus) in daily speaking (quotidianus) and was perceived as lower-class (plebeius)."
https://en.wikipedia.org/wiki/Vulgar_Latin
Wiki:
"Philological analysis of Archaic Latin works, such as those of Plautus, which contain snippets of everyday speech, indicates that a spoken language, Vulgar Latin (sermo vulgi ("the speech of the masses") by Cicero), existed at the same time as the literate Classical Latin. The informal language was rarely written, so philologists have been left with only individual words and phrases cited by classical authors and those found as graffiti."
https://en.wikipedia.org/wiki/Latin
Wiki:
"The written Latin of today, as used for Church purposes, does not differ radically from classical Latin. Study of the language of Cicero and Virgil suffices adequately for understanding Church Latin."
https://en.wikipedia.org/wiki/Ecclesiastical_Latin#Compariso...
And finally, to quote what I quoted another user in this thread:
"But you are right, Cicero is Classical Latin. However, we were taught a mix of Latin that is kind of like what this Wiki says:
'The Latin of the panegyrics is that of a Golden Age Latin base, derived from an education heavy on Cicero, mixed with a large number of Silver Age usages and a small number of Late and Vulgar terms.'
https://en.wikipedia.org/wiki/Panegyrici_Latini#Language_and...
'Silver Age' is what I probably should have said instead of strictly Late and Vulgar, which are both technically different terms, but which were also taught in my Latin courses."