A chromatic scale is a scale that contains all of the notes in an octave (twelve semitones). Arnold Schoenberg, a 20th century composer, used this little bit of theory to create a technique called "dodecaphony" or the twelve-tone technique. He'd essentially create a musical piece in which each note of a chromatic scale was used the same number of times as every other note and no note had more emphasis than the others (the idea of the piece of music being in any key is erased). This concept is paramount to the work of a lot of 20th century composers. I believe his work was also dubbed "degenerate" by Nazis during WWII.
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