Pentatonic scales.
These are 5 note scales, of which there are many, however only two are common in jazz and I will refer to them as the major and minor pentatonic.
The major pentatonic is the same as the major scale but without the 4th or 7th (ex 11d-1). It is common in western folk music and is often used by composers to impart a traditional flavour (Amazing Grace, Auld Lang Syne)
The minor pentatonic is the same as the Aeolian or Dorian scale but without the 2nd or 6th (Ex 11d-2). This scale is sometimes used by composers to give an oriental feel.
jazz theory
ex 11d: Pentatonic scale
These scales can be very easy to use as they can be fitted over many chords without wrong notes, but they can become monotonous. Used very effectively by Sonny Rollins and John Coltrane.