The B flat diminished seventh chord is a 4-note chord consisting of the notes Bb, Db, Fb and Abb.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Bbdim7.
Interactive piano diagram for the B flat diminished seventh chord
Chords that are a subset of Bbdim7. These contain less notes but all of them are included in Bbdim7.