Two musical notes which are eight tones apart on a scale are an example of an octave.
An octave key.
The melody jumps up an octave at the beginning, then later drops back down an octave.
The singer was known for astounding clarity over her entire five-octave range.
The octave has a pitch ratio of 2:1.
The bass starts on a low E, and the tenor comes in on the octave.