1The outer side, surface, or area of something, as opposed to the inside; the exterior. The most basic spatial antonym of 中 (inside).
窓の外を見ると、雪が降っていた。
When I looked outside the window, snow was falling.
この箱の外側には何も書かないでください。
Please don't write anything on the outside of this box.
ドアの外で誰かが立っている気配がする。
I sense someone standing outside the door.
外から見ると小さな店だが、中はとても広い。
It looks like a small shop from the outside, but it's very spacious inside.
2Outdoors; the open air, as opposed to being inside a building. Used when talking about being out, going out, or the weather outside.
今日は天気がいいから、外でお弁当を食べよう。
The weather is nice today, so let's eat our bento outside.
子どもたちは外で元気に走り回っている。
The kids are running around energetically outside.
外は寒いから、コートを着て行きなさい。
It's cold outside, so wear a coat when you go out.
雨が降ってきたから、洗濯物を外に干したままにしないで。
It's started to rain, so don't leave the laundry hanging outside.
3A place, person, or organization outside one's own home, company, or group; the outside world, outsiders, or somewhere other than one's familiar circle.
家のことは外では話さないようにしている。
I try not to talk about family matters outside the home.
この件は外に漏らさないでください。
Please don't let this matter leak to outsiders.
うちの会社のやり方は、外ではあまり通用しない。
Our company's way of doing things doesn't really work elsewhere.