A pentatonic scale is a musical scale with five notes per octave, in contrast to the more familiar heptatonic scale that has seven notes per octave (such as the major scale and minor scale).

Pentatonic scales were developed independently by many ancient civilizations—an indication that pentatonic scales are based upon a naturally occurring phenomenon. They are still used all over the world, for example (just to name a few) Chinese traditional music and US country music and blues.

There are two types of pentatonic scales: those with semitones (hemitonic) and those without (anhemitonic).

Source: Pentatonic scale – Wikipedia