Chord-melody is the approach to guitar playing where both the chord and melody are played at the same time. Although mastering this form of guitar playing is very difficult, a well-rounded guitarist should have at least a basic understanding of this guitar style. There was a great article in the October 1994 issue of Guitar Player entitled "Chord Melody Concepts" by Joe Pass. There was also an earlier article in the July 1976 issue of Guitar Player entitled "Chord Melody" by Arnie Berle. The best commercial site is Chord Melody Guitar Music.
To get you started, below is an example of a possible chord-melody sketch for the A section to Hoagy Carmichael's 1930 standard Georgia On My Mind in the key of C.