Well, "copyright" as in "this work may not be copied, published, distributed or microfilmed without prior written consent of the holder" or whatever the full legal text is. Fonts and glyphs are intellectual property, works of art sometimes, and are by default protected by copyright. So are all your texts that describe how it all works.
You have the option to go copy-left, GNU, DBAD, whatever. But that must be explicitly stated in a license text.
https://en.wikipedia.org/wiki/Intellect ... _typefaces