The A dominant seventh (A7) guitar chord only uses 5 strings. The sixth low E string is not played.
The 5th (A) string
is open
The 4th (D) string is fretted at the 2nd fret.
The 3rd (G) string is open.
The 2nd (B) string is fretted at the second fret.
The 1st (E) string is open.
