Octave

In music, an octave (Latin: octavus: eighth) or perfect octave (sometimes called the diapason) is a series of eight notes occupying the interval between (and including) two notes, one having twice or half the frequency of vibration of the other. The octave relationship is a natural phenomenon that has been referred to as the "basic miracle of music", the use of which is "common in most musical systems". The interval between the first and second harmonics of the harmonic series is an octave. In Western music notation, notes separated by an octave (or multiple octaves) have the same name and are of the same pitch class.

To emphasize that it is one of the perfect intervals (including unison, perfect fourth, and perfect fifth), the octave is designated P8. Other interval qualities are also possible, though rare. The octave above or below an indicated note is sometimes abbreviated 8^a or 8^va (Italian: all'ottava), 8^va bassa (Italian: all'ottava bassa, sometimes also 8^vb), or simply 8 for the octave in the direction indicated by placing this mark above or below the staff.