[yakubin]

Italian, not Latin. Italian is the language of music. Italy used to be the capital of European music. That's where it comes from. I also wouldn't classify it as mere "theory". It's basic notation that appears in notes. Calling it "theory" is like calling control flow constructs in Pascal (the language) "theory".

[noobly]

It's called music theory though? I agree it's a bad name, but that's what it's called..

[chuchana]

It is. This video argues it would be more accurate to call it the harmonic style of 18th century European musicians: https://www.youtube.com/watch?v=Kr3quGh7pJA