“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—Music notation for everyone http://www.lilypond.org]

Other proprietary and free engraving (or “notation”) programs, like MuseScore and Denemo, focus on the visual aspects of musical scores, LilyPond focusses on the semantic aspects. Because LilyPond is a text-based music engraving program, the separation between meaning and appearance is similar to HTML and CSS. Web developers use HTML to tell web browsers what an object means (a <title> tag tells a browser that some text is a title, for example), and CSS to tell web browsers how objects with different meaning should look (that all titles are blue, for example). The LilyPond language does not look like HTML and CSS, but you may have a similar experience. LilyPond users use letters and numbers to tell LilyPond what a note means (a “g4” is the pitch G with a quarter-note duration, for example), and can change the visual appearance if they wish (by using a square notehead, for example).

Advanced LilyPond users can, for example, incorporate scores into LaTeX and HTML documents; create new musical symbols and notation styles using the Scheme programming language; and tweak output quickly and flexibly with SVG-format output.