A scale is a series of notes spanning an octave that are arranged in ascending or descending order and forming the basis for the melodies and harmonies used in music. This pattern of intervals (spaces between notes) is the same for all octaves in a scale, regardless of the note on which they begin (tonic).
There are many different scales, varying according to the number of notes they contain and the sizes of the intervals. Most Western music of the past several hundred years uses major and minor scales, which are forms of heptatonic scales (seven notes per octave). Heptatonic scales, in turn, are based on the chromatic scale, which is a series of twelve pitches in each octave.
The notes in the scales commonly used in Western music are named with the first seven letters of the alphabet, and the name of any scale includes the name of its first note. For example, the notes of the C major scale, which begins on middle C, are C, D, E, F, G, A, B, and C. On a piano, these are all the white keys between the two C's. The intervals between any two adjacent notes are two half steps, except for between E and F and between B and C for which they are a single half step. With this scale, the the third and fourth notes and the seventh and eighth notes will always be separated by a single half step regardless of the note on which the octave is begun, although some of the notes will be black keys when beginning on other notes.