https://www.musical-u.com/learn/listening-for-diminished-triads/
Maybe you are listening to your favorite band playing a tune on the radio, jamming out with your heavy metal band, or just trying to figure out what chords work underneath the saxophonist’s jazzy riff, when suddenly you hear a chord that’s not quite a minor chord.
What could it be? Well, it might just be a diminished triad: https://www.musical-u.com/learn/listening-for-diminished-triads/