The Collaborative International Dictionary of English v.0.48:
off-street \off-street\ adj. Not performed on the streets; as, off-street parking; off-street unloading of vehicles. Opposite of on-street. [WordNet 1.5]WordNet (r) 3.0 (2006):
off-street adj 1: not on the streets; "off-street parking"; "off-street unloading of vehicles" [ant: on-street]