B Diminished (Bdim)
1+b3+b5
Notes in B Diminished
B (root)DF
Inversions
Same notes as B Diminished, with a different chord tone as the lowest note. Useful for smoother movement between chords instead of jumping around the keyboard.
Root position
B in the bass
1st inversion
D in the bass (Bdim/D)
2nd inversion
F in the bass (Bdim/F)
Press B, D and F together on the keyboard and you're playing B Diminished.
Stack two minor thirds and the fifth shrinks along with the third, producing a triad that never feels at rest. Diminished chords are unstable by design, built to lean somewhere else, usually resolving up by a half step. Played alone it can sound almost comical, but tucked between two other chords it's one of the most useful tension devices in tonal music.