The C fifth chord is a 2-note chord consisting of the notes C and G.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as C5.
Chords that are a superset of C5. The chords include more notes but always C and G.
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 C5 chord. Feel free to save or share the image as needed.