This refers to a specific chord or key.
☛ A. When it refers to a chord, then the chord has three musical pitches with the space between the first and second pitches being four half steps, and the distance between the second and third pitches being three half steps. A half step is the smallest interval (space or distance) in traditional western classical music. It is the distance from any key on the piano to the closest adjoining key (white or black).
☛ B. When major refers to a key, it is the central tonality upon which a work or movement is constructed, and will usually use the same tonic chord as the central or “destination” chord of the composition. For example, the Schumann Symphony No. 3 is in the key of E-flat major, and the first and last movements begin and end in the key of E-flat. Of course many keys and chords are used throughout this five movement work, but the most prominent one is E-flat.