A chromatic scale consists of an ascending or descending sequence of 12 pitches, each a semitone or a half step apart.
The term chromatic derives from the Greek word chroma, which means color.
A chromatic scale can be played on the piano by using all black and white keys in order, without leaving any out.
The structure of a chromatic scale is therefore simple and uniform (all notes being separated by semitones), unlike major and minor scales which have tones and semitones in particular arrangements.
Study in C Major, Op. 45, No. 16
Study in A minor, Op. 84, No. 8