at sort1 (10)word choice word choice out, outside, outdoors, out of doorsIf you are out, you are away from a building, especially the place where you live or spend a lot of time• Debbie's out. She'll be back later. • Why don't we go out for the day?If you are outside a room or building, you are not in it but are close to it• Meet me outside the library. • I sat on a chair outside his office. • You'll have to wait outside in the corridor.When outside is an adverb, it can also mean 'not inside any building'• It's cold outside.Outdoors or out of doors always mean 'not inside any building'• We usually spend summers outdoors. • I like weddings that are held out of doors.!! Do not confuse outdoors (with an -s) and outdoor (without an -s). Outdoors is an adverb• I like playing outdoors. Outdoor is an adjective that can only be used before a noun• outdoor activities such as fishing
Definition from the Longman Dictionary of Contemporary English Advanced Learner's Dictionary.