Octave comes from the Latin root “octo,” meaning eight. An octave represents the interval from one musical pitch or note to another. It is the distance from one note to the next note of the same name. It takes eight white keys to get to the next latter-named note, hence why we call it an octave.
How are piano octaves numbered?
In scientific pitch notation, a specific octave is indicated by a numerical subscript number after note name. In this notation, middle C is C4, because of the note’s position as the fourth C key on a standard 88-key piano keyboard, while the C an octave higher is C5.