guitar chord
C♯dim
Two minor thirds stacked. The fifth is diminished, so it cannot be dropped without losing the chord.
Written the other way round it is D♭dim — the same twelve keys on a piano, a different piece of notation.
Every fingering that fits a hand
x45050
easy
x42020
easy
x42050
easy
x45020
easy
x42023
moderate
What is true of it
C♯dim is C♯, E and G — 1, b3 and b5 counted from C♯.
The easiest of the 5 fingerings below is x45050: 3 fingers, held at the 4th fret.
None of them uses an open string, so this chord moves up the neck unchanged — the same shape 1 fret higher is the chord a semitone above.
1 string stays silent.
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
C♯dim/E
045050
C♯dim/G
342020
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.