A D# Diminished (D#dim) chord contains the notes D#, F#, A. It is built from the diminished formula 1 - ♭3 - ♭5, with D# as the root.
Why are diminished chords called symmetrical?
Because they're built from two stacked minor thirds, every note is the same distance apart. That means the same shape repeats every three frets, and any note in the chord can act as the root — which is why one form covers so many chords.