UK:*UK and possibly other pronunciationsUK and possibly other pronunciations/ˌaʊtˈsaɪd/

US:USA pronuncation: IPAUSA pronuncation: IPA/n. ˈaʊtˈsaɪd, -ˌsaɪd; adj. ˌaʊtˈsaɪd, ˈaʊt-; adv. ˌaʊtˈsaɪd; prep. ˌaʊtˈsaɪd, ˈaʊtˌsaɪd/

US:USA pronunciation: respellingUSA pronunciation: respelling(n. outsīd, -sīd′; adj. out′sīd, out-; adv. out′sīd; prep. out′sīd, outsīd′)

WordReference Collins English Usage © 2020
Outside can be a preposition or an adverb.
used as a preposition
When someone or something is close to a building but not actually inside it, you say that they are outside the building.
I parked outside the hotel.
There are queues for jobs outside the main offices.
Be careful
Don't say that someone is ‘outside of’ a building.
used as an adverb
You can also say that someone or something is outside or that something is happening outside.
The shouting outside grew louder.
Please could you come and fetch me in 20 minutes? I'll be waiting outside.
When you go outside, you leave a building and go into the open air, but stay quite close to the building.
When they went outside, snow was falling.
Go outside and play for a bit.
If you leave a building in order to go some distance from it, don't say that you go ‘outside’. Say that you go out.
When it got dark he went out.
I have to go out. I'll be back late tonight.
You can also say that someone is outside when they are close to a room, for example in a hallway or corridor.
I'd better wait outside in the corridor.
another meaning of ‘outside’
You can also talk about someone or something being outside a country. When outside is used like this, it does not have ‘near’ as part of its meaning. If you are outside a country, you can be near the country or a long way away from it.
You'll know this if you have lived outside Britain.
'outside' also found in these entries:

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