The 12-bar blues is a musical structure commonly used in blues music, consisting of 12 measures or bars. It typically follows a specific chord progression, often using the I, IV, and V chords of a key. This format provides a framework for musicians to improvise and express emotions, making it a staple in various genres, including rock and jazz. In a standard 12-bar blues progression, the first four bars usually feature the I chord, followed by two bars of the IV chord, two more bars returning to the I chord, and then one bar each of the V, IV, and I chords. This simple yet effective structure allows for creativity and variation in performance.