The “blue” note is a note outside the Pentatonic Scale that allows for the most authentic tension and release available in the blues sound. The blue note, in between the fourth and fifth interval of the Pentatonic Scale, is technically referred to as the flat 5 note, as it’s found by flattening the fifth of the scale. By including this note in the Pentatonic Scale, you end up forming a new scale known as the Blues Scale.
The downloadable Blues Scale diagram, featured on the great site Free Guitar Source, outlines the five new positions of the Blues Scale if you’re inclined to adapt them. You’ll find this one little note will completely transform your phrases and allow you to tap in to your bluesy emotions you may be harboring.