Origins of garage and parking space (3)
I believe the answer is:
'space' is the definition.
(gap is a kind of space)
'origins of garage and parking' is the wordplay.
'origins of' says to take the initial letters.
The first letters of 'garage and parking' is 'GAP'.
(Other definitions for gap that I've seen before include "Cleft", "A small parting, in hedge or teeth", "Aperture", "Room", "A breach or pass".)