The 12 Bar Blues is a pattern of chords which repeats every 12 bars. It is the most common progression in Blues music, and is used extensively in Rock and Jazz as well. In this lesson there are two examples of 12 Bar Blues in the key of C.
Both progressions make use of the chords C, F and G in the right hand part. The left hand part contains a Bb note, which is not one of the notes of any of the chords here. This note comes from the Blues Scale, which will be discussed in detail later in the book.