Musical intervals are simply the distance between any two notes, such as 2nds, 3rds, 4ths, 5th, etc. But each intervals has a quality of being either major or minor or diminished or augmented or perfect. Intervals occur as melodic intervals and harmonic intervals. Interval names remain constant no matter what the key signature. A knowledge of music theory including music intervals is beneficial when it comes to ear training as well.

Intervals HD from chordman on Vimeo.