A pedal point is a sustained tone that is played while chords move from one to another. This is typically played in the bass or lowest pitch. The playing of a pedal point creates tension as the chords move but the pedal tone stays the same thus creating a non chord tone being played under a chord. By creating tension in your music it stimulates interest in the ear as the listener awaits the resolution or release of the tension.
Learn more about pedal points and see some examples here