Chord Pong 7! B half diminished to C major 7 - Major Scale
The last set of transitions in the major scale!
These chords come from the collection of notes that make the major scale, each note having harmonies, which in turn make the chords.
This is how key signatures work for songwriters who would like to understand why there's only so many chords to choose from in a key they'd like to write in, even though theory is for the privileged school folk. (You have to like this video if I'm describing your situation!) Peace be the jams! B D F A goes to C E G B