The A dominant seventh chord is a 4-note chord consisting of the notes A, C#, E and G.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as A7.
Chords that are a superset of A7. The chords include more notes but always A, C#, E and G.
Chords that are a subset of A7. These contain less notes but all of them are included in A7.
In case you prefer a non-interactive variant of the chord chart, we've embedded a PNG image below that shows the notes for the the A7 chord. Feel free to save or share the image as needed.