Definition: the original text of something; esp. music
“ur-” is German for “original” or “primitive.”
The urtext is the original document, without any changes. It’s often used to discuss printed music, as these tend to change over time to accommodate new notation or musical styles.
Why I Looked It Up
From The Real Work, discussing the mythical S.W. Erdnase, a pen name adopted by the author of a seminal book on card tricks.
Erdnase is everywhere. […] He is the subtext, and sometimes the ur-text, of so much else.
Note that I didn’t find the hyphenation anywhere else when researching this.