A pentatonic scale is a musical scale or mode with five notes per octave in contrast to a heptatonic (seven note) scale such as the major scale and minor scale. Pentatonic scales are very common and are found all over the world. They are divided into those with semitones (hemitonic) and those without (anhemitonic).
The word "pentatonic" comes from the Greek word pente meaning five and tonic meaning tone. Simply put, the pentatonic scale consists of five notes within one octave, that's why it is also sometimes referred to as a five-tone scale or five-note scale. It is believed that the pentatonic scale was used way back in ancient times. Composers like Claude Debussy have used pentatonic scales for added effect in his music.
The anhemitonic form of pentatonic scale has no semitones (ex. c–d–f–g–a–c} this is the most commonly used form.
The two basic forms of pentatonic scales are:
Major Pentatonic - Consists of the 1st - 2nd - 3rd - 5th - 6th notes of a major scale.
Minor Pentatonic - Consists of the same 5 notes of a major pentatonic scale but its tonic (first note of the scale} is 3 semitones below the tonic of the major pentatonic scale. For example, the C major pentatonic (C - D - E - G - A} has the same notes as the A minor pentatonic (A - C - D - E - G} but arranged differently. The first note or tonic of the A minor pentatonic scale (=A) is 3 semitones (half steps) lower than the first note of the C major pentatonic scale (=C). It uses the 1st - minor 3rd - 4th - 5th - minor 7th notes of a scale.