What is a harmonic interval?
Answer: Notes that are played together or simultaneously create harmony. The interval between these notes are called harmonic intervals. Just like melodic intervals, there are harmonic 2nds, 3rds, 4ths, 5ths, 6ths, etc. The difference is that in melodic intervals the notes are played one after another, while in harmonic intervals you play the notes at the same time.
Notes on a chord that are played together have harmonic intervals. The most common type of chords are major and minor chords. The triad is a type of major or minor chord that has 3 notes played either at the same time or one after another. A major triad is played using the 1st (root) + 3rd + 5th notes of a major scale. A minor triad is played using the 1st (root) + 3rd + 5th notes of aminor scale.