The Bdim7 chord (diminished 7th): notes B D F G#, degrees 1 – ♭3 – ♭5 – ♭♭7. Guitar shapes: x20101, 78676x, 789797, x-x-9-10-9-10.
A chord is the root plus degrees above it, most often stacked in thirds. Major and minor differ only in the lower third: a major third (M3) sounds bright, a minor third (m3) sounds sad. Pick a chord and a root to see its degrees and intervals, and its shapes.
m — minor, M — major, P — perfect, A — augmented interval; the number is the degree count. m3 is 3 semitones, M3 is 4, P5 is 7
B Bm B5 B7 Bm7 Bmaj7 Bsus2 Bsus4 Badd9 B6 Bm6 B9 Bdim Bdim7 Bm7♭5 Baug