Guitar chords: D diminished seventh
Ddim7
 XXO O
 ======
 |||1|2  1st fret
 ------
 ||||||
 ------
   DACF
    bb

Notes: 1  : D 
       m3 : F
       d5 : Ab  
       bb7: Cb
These diminished chords all have the same notes as each other: Fdim7, Abdim7, Bdim7, and Ddim7.