Another type of common chord is called the "dominant seventh" chord. It is usually referred to as the "seventh" chord. The chord symbol for the seventh chord is the number 7 written after the alphabetical letter. The symbol for a D seventh chord is D7.
D7
To play the D7 chord, place the first, second and third fingers of your left hand as shown in the diagram, but strum only five strings. Do not strum the 6th string (as indicated by the striped line).