Definition:Vulgar Fraction/Linguistic Note

Linguistic Note on Vulgar Fraction
The original everyday meaning of the word vulgar was at one point common, in the sense usual or everyday.

It derives from the Latin vulgus, meaning the common people in the sense of the public.

Through the process of the euphemism treadmill, the word in natural language has since gained the meaning rude or impolite.

Incidentally, it is also worth noting that the word common has gone the same way.