G Major 6th
6
0 - 4 - 7 - 9Major + major 6th
About G Major 6th
G6 is a G major chord with an E added — and on guitar that addition costs nothing, because the open high E string is already there. Strum a three-finger G without muting anything and you have very nearly played it. That accident is why the chord appears constantly in country and swing without anyone calling it by name.
The notes
G, B, D, E. The E is a major sixth above the root, and unlike a seventh it does not create tension — it fills the chord out and leaves it stable. A G6 can end a song where a G7 cannot.
The same four notes read from E give E minor seventh. Whether the ear hears G6 or Em7 depends entirely on which note the bass is playing, and that ambiguity is useful: arrangers slide between the two without changing a finger.
On the fretboard
The simplest shape keeps the standard G and lets the high E ring open instead of fretting it at the third fret. One finger less than the four-finger G, and a different chord.
The swing voicing puts the sixth in the middle of the chord rather than on top, which sounds tighter and suits a rhythm part played with a pick close to the bridge.
Where it shows up
Country, western swing and rockabilly use the sixth as a default ending: a G6 held under a final chord sounds finished but not formal, which suits the idiom.
In jazz it appears as a tonic substitute — Gmaj7 is smoother, G6 is drier, and the choice between them is a matter of era as much as taste.