The distance between two musical pitches is called an interval. Intervals are important to music because they build scales and chords. In other words, music gets its richness from intervals. Composers and musicians use two types of intervals: harmonic and melodic intervals.
You get a harmonic interval when you play two notes at the same time.
You get a melodic interval when you play two notes separately in time, one after the other.
The identity of both harmonic and melodic intervals is determined by two things:
Quantity: You determine an interval's quantity by simply adding the lines and spaces included in the interval on the music staff. Accidentals (sharps and flats), which raise or lower a pitch by a half step, don't matter when counting interval quantity. Interval quantity may be
Unison (or prime)
Quality: Interval quality is based on the number of half steps from one note to another. Unlike in interval quantity, accidentals do matter in interval quality. The terms used to describe quality, and their abbreviations, are as follows:
Major (M): Contains two half steps between notes
Minor (m): Contains a half step less than a major interval, or one half step between notes
Perfect (P): Refers to the harmonic quality of primes, octaves, fourths, and fifths
Diminished (dim): Contains a half step less than a minor or perfect interval
Augmented (aug): Contains a half step more than a major or perfect interval