Twelve-bar blues is a type of music that follows a particular pattern. It has 12 different bars (or measures) in the music. Each bar usually has 4 beats. In the 12-bar blues, the first bar (the first 4 beats) is a certain chord, then the next 4 beats are a different chord, and then another different chord for the last 4 beats. This pattern gets repeated 3 times, until all 12 bars are done. This helps make the music feel catchy and easy to remember.