Including a glossary for a fantasy or science fiction epic is standard practice. Tucked away at the end of a book, they are useful references if you have set a book aside for a while and need to re-familiarize yourself with the language and culture of a story.
My first copy of the Lord of the Rings was a massive, hard-bound copy I checked out from the Public Library. It included all three books, a biography of Tolkien, and a glossary that rivaled the Silmarillion. I had a special bookmark for the glossary and often lost myself tracing entries while assembling Middle Earth in my head.
Another epic that included a glossary at end of each book was The Wheel of Time. Here, though, the glossary tried to contain itself to the book at hand. Occasionally there was a term I was unfamiliar with. If it was not in the current book’s glossary, I would have to dig out an older book to find it, or read on, hoping the story would remind of the term’s meaning.
I wrestled with including a glossary with The Fundamentals and decided against it. The world is a different place since Jordan and Tolkien published their novels on paper. As I write this, I am reading The Handmaid’s Tail in paperback and am surprised how different the dynamics are from reading on my Kindle. My earliest outlines of The Walking Circle website included a glossary section for Martial Art terms, and I have carried that forward with my fictional writing. This gives me a lot more flexibility over including the terms in a book. Without further ado, here is the initial pass at my fictional glossary.