piano chord
G6
G1B3D5E6
A major triad with a sixth added. The same four notes as a minor seventh chord a third below.
What is true of it
G6 is G, B, D and E — 1, 3, 5 and 6 counted from G.
These are also the notes of Em7/G. Which name is right depends on what is underneath and what came before — the notes alone do not decide.
On an instrument that cannot reach all 4, the 5 goes first, in that order.