{lilypond} is for questions addressing issues related to the LilyPond software in connection with TeX and friends. Use it for questions concerning the lilypond-book program or other ways for making LilyPond and TeX to interact with each other.
LilyPond is a music engraving program, devoted to producing the highest-quality sheet music possible. It brings the aesthetics of traditionally engraved music to computer printouts. LilyPond is free software and part of the GNU Project. Questions about the lilypond-book program, which incorporates LilyPond and (Xe)LaTeX fall under this tag as well as other questions about interactions between LilyPond and TeX programs.
Related to musicology the author mentioned in this question favored LilyPond in 2020 wrt overall workflow, to include e.g. functional analysis: Are there similar documents in English about "How to integrate music examples with open source tools in scientific documents"?