Musical intervals (7)
I believe the answer is:
octaves
'musical intervals' is the definition.
(octave is a kind of musical interval)
This is all the clue.
(Other definitions for octaves that I've seen before include "Musical intervals of eight notes" , "lot of notes" , "Eight-note spans" , "8-note hand spans (mus.)" , "Groups of eight consecutive notes on a scale" .)