Pentatonic Scales are scales that have five notes. There are many possible Pentatonic scales but the most common ones are the "Major" Pentatonic and the "Minor" Pentatonic.
The "Major" Pentatonic scale has this interval pattern:
The "Minor" Pentatonic scale has this interval pattern:
If you play only the black keys of a keyboard you are playing a pentatonic scale.
Learn about more Scales