Definition of backstretch:
(n) :
(athletics, horse racing, car racing) Synonym of back straight (“straight part of a racetrack, running track, etc., opposite the finishing line”).
(n) :
(horse racing) An area next to a racetrack used to stable the racehorses and house employees.
(n) :
(exercise) An exercise that stretches the muscles of the back.
(n) :
(figuratively) The middle part of an event.