The major scale (or Ionian scale) 

is one of the most commonly used musical scales, especially in Western music. It is one of the diatonic scales. Like many musical scales, it is made up of seven notes: the eighth duplicates the first at double its frequency so that it is called a higher octave of the same note (from Latin "octavus", the eighth).  

 Relationship to major keys If a piece of music (or part of a piece of music) is in a major key, then the notes in the corresponding major scale are considered diatonic notes, while the notes outside the major scale are considered chromatic notes. Moreover, the key signature of the piece of music (or section) will generally reflect the accidentals in the corresponding major scale.  

For instance, if a piece of music is in E♭ major, then the seven pitches in the E♭ major scale (E♭, F, G, A♭, B♭, C and D) are considered diatonic pitches, and the other five pitches (E♮, F♯/G♭, A♮, B♮, and C♯/D♭) are considered chromatic pitches. In this case, the key signature will have three flats (B♭, E♭, and A♭).  The figure below shows all 12 relative major and minor keys, with major keys on the outside and minor keys on the inside arranged around the circle of fifths. weki