1Outside or in the open air; outdoors (not inside a building).
子供たちは戸外で元気に遊んでいる。
The children are playing energetically outdoors.
運動会は戸外で行われる予定だ。
The sports day is scheduled to be held outdoors.
寒いので長時間戸外にいるのは避けたほうがいい。
It's cold, so you should avoid staying outside for long periods.