In the middle of; in the midst of; in the course of. Used as 〜の最中(に) to indicate something is happening right at that moment.
会議の最中に突然停電した。
There was a sudden power outage in the middle of the meeting.
食事の最中にスマホを見るのはやめてほしい。
I wish you'd stop looking at your phone in the middle of meals.
引っ越しのさなかで部屋が散らかっている。
The room is a mess because we're in the middle of moving.
試合の最中に雨が降り出した。
It started raining in the middle of the game.