A chord chart is a song written out as lyrics with the chords marked above (or inline with) the words they change on, rather than full musical notation.
It's the format most gigging musicians actually read from, because it shows exactly what to play and sing without needing to read music.
In Songhub, a chord chart is also live data rather than a flat page — it can be transposed to a new key, adjusted for a capo, and reused across multiple setlists.