guitar chord
C5
C1G5
Root and fifth, no third at all — neither major nor minor, which is the point.
What is true of it
C5 is C and G — 1 and 5 counted from C.
No fingering of C5 fits a hand on the guitar: inside four frets, with the strings that sound next to each other and the root underneath, there is nothing to hold.
Where its notes are on the neck
The brass dots are C, the root. Everything else is a chord tone with its degree printed in it.
With a different note underneath
C5/G
3350xx
An inversion is the same chord with a different note lowest. The name changes to a slash name because the bass is what a listener hears as the foundation.