Retrace one's steps (5)
'retrace one's steps' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for backtrack that I've seen before include "Return, retract" , "Reverse (opinion)" , "Retrace one's steps" , "Climb down" , "Withdraw" .)
(Other definitions for track that I've seen before include "path to follow" , "A prepared course for racing on" , "Sign that one's passed" , "one of a number on record" , "Racing circuit" .)