A LeadSheet is a simplified version of a song, usually stating the melody and chord changes. This primarily exists in non-classical Western music. Different genres have personalized notation as well: country music, especially the Nashville studio scene, relies on a number system (very similar to a Roman numeral system). Jazz and pop, however, tend to list chords by name. Most lead sheets give no order or arrangement in regards to performance; rather, it is up to the user to determine these factors plus instrumentation. The most significant contributors to jazz lead sheets are the Real Book (published originally from Berklee School of Music, but fairly inaccurate) and the Jamey Aebersold series (comparatively adheres to more common keys for standards). 
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Surely there is something analagous to this in the programming world:  a roadmap of a program?  Non-programmer talking here.
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In the programming world, a .h file would be an example of a LeadSheet -- a simplified version of the actual code, providing a very high-level view of it.