Pentatonic Scale Theory Things   William Wieland
Strictly speaking, a pentatonic scale is simply a 5 tone scale. However, a pentatonic scale usually refers to a major pentatonic scale;
1 - 2 - 3 --- 5 - 6 --- (1) of a major scale or do - re - mi --- sol - la --- (do). The intervals are M2 - M2 -- m3 -- M2 -- m3.
To create a pentatonic scale, simply remove the 4th and 7th notes of a Major Scale.
C major scale
  C pentatonic scale
(C major pentatonic scale)
E flat major scale
  E flat pentatonic scale
A major scale
  A pentatonic scale
Bobby McFerrin Demonstrates the Power of the Pentatonic Scale
The black keys on the piano are an F sharp (or G flat) major pentatonic scale.
Piano Pages:  Pentatonic Playing by Ear   Pentatonic Improvising