From a theoretical point of view, (western) music is essentially made up of twelve tones. These 12 tones are sometimes called the chromatic scale. We use the first seven letters of the alphabet in conjunction with some other symbols to represent these tones which are commonly called notes.

The chromatic scale is a musical scale with twelve pitches, each a semitone, also known as a half-step, above or below its adjacent pitches. As a result, in 12-tone equal temperament (the most common tuning in Western music), the chromatic scale covers all 12 of the available pitches.

Put simply, a chromatic scale is all 12 notes arranged in ascending or descending order of pitch. It’s made up entirely of half steps (semitones), with each note being a half step above or below the last note.