A Pentatonic scale is simply a scale containing 5 notes.

Traditional scales such as major scales or modal scales contain 7 notes. When you use a scale which has 5 notes, it tends to generate more power than scales which have more notes. Scales with more notes tend to generate more color. 

Rock, Blues and Country often fall into the Pentatonic category. Jazz tends to fall into the 7 or more note category. This being said, any form of music has the potential to use scales of any number of notes. The effect is what you seek with your choice of scales.

Of all the many Pentatonic scales, the following 5 can be considered the “main” Pentatonic scales:

C D E G A C = 1, 1, 1+ 1/2, 1, 1+ 1/2  Major Pentatonic

C D F G Bb C = 1, 1+ 1/2, 1, 1+ 1/2, 1  Suspended Pentatonic

C Eb F Ab Bb C = 1+ 1/2, 1, 1+ 1/2, 1, 1 Sub Dominant Minor Pentatonic

C D F  G A C = 1, 1+ 1/2, 1, 1, 1+ 1/2  Sub Dominant Major Pentatonic

C Eb F G Bb C = 1+ 1/2, 1, 1, 1+ 1/2 , 1  Minor Pentatonic