A diagram that shows where to place your fingers to fret a given chord. Chord charts usually show the first few frets. Sometimes the chord shown is played further up the neck. In that case, text next to the chart will show which fret the chart starts with.
A chord chart is a simplified text document that typically represents lyrics with ASCII chord symbols placed above the appropriate syllables of the lyrics to associate the relative timing of the chord changes to the words of a song. Musically speaking, chord charts really represent an arrangement (albeit with many elements lacking) of a song, rather than a true song in complete content. This is because a complete representation of a song is a musical composition made for the human voice, which will always include notation for pitch and timing.