The link above is to my textbook on music terminology
Music Theory is not the same as Music Terminology.
People usually misunderstand what music theory is. They incorrectly believe that studying chord names, rhythms, and music notation is the same as studying music theory, but it is not. That is just music terminology, which is the language we use to contruct music. Music theory on the other hand, is quite simply, a theory. A theory is like any of Newton's 3 laws of motion. It's an idea that we think is true. We test a theory by hypothesizing the outcome of an experiment based on the theory. If the hypothesis comes true, it's more support that the theory is correct. Entire areas of academic study are built off of a few foundational theories.
So what kinds of music theory are there? There are two major ones, classical theory & jazz theory. Classical theory is built off the belief that once a tonic has been established, our mind expects any move to the dominant to return back to the tonic. Off that one simple idea, a huge amount of knowledge has been contributed to the subject. In fact, even the layout of our piano was heavily influenced by classical theory.
Classical Music the genre and Classical Theory are not the same.
Classical music as a genre, is defined mostly by the sounds and rhythms it uses. It has less to do with the use of classical theory, which focuses on the progression of pitches.
Classical music also refers to a specific style and even an era of music, whose two most famous composers were Mozart & Beethoven. Many people incorrectly believe that any music performed by an orchestra is classical music, but that's wrong. Other famous genres that are often performed by orchestras are Baroque, Romanticism, Impressionism, Serial, Futurism, Neoclassical, Minimalism, and Post-Minimalism. Genres are not academic areas of study though because they are vocational. That would be like getting a degree in how to a use a calculator instead of a degree in mathematics.
Why did I write this book?
Classical and jazz theory do a terrible job of explaining a lot of music that's been made over the past 50 years or so. That being said, when I studied music, I just wanted to learn a set of music terminology that could explain everything I was listening to without trying to apply a music theory to it. That way, when it came time to write or play music with other musicians, we would have the terms to communicate our musical goals easily. That's mostly what my textbook tackles. It's like a grammar book for music.
Will I ever expand it?
Maybe. There's a lot in the book that I'm sure needs an explanation for academics in music to trust it. I'd like to write that explanation for a journal in a near future. I'd also love to write a book on my own music theories. While I do believe in the dominant function of classical theory and the subtonic function of jazz theory, I think that those are only two of several music theories needed to explain the wealth of music that has exploded in the past century. Writing that book though, will be a huge effort.