Open For Business
noun
Remember how 営業 means "business"? Well, if you're in the middle of running a business, it means you're open for business.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well. It will help to know 営業 first as well.
今日は日曜日なのに営業中なんですね。
It's open for business today, isn’t it, even though it's Sunday.
営業中に電話しないでって言ったじゃない。
I asked you not to call me when the shop is open.
営業中にお客さんの前でヒジをつくなんて、一流のホストだったらありえないよ。
It's unthinkable for a top-class host to lean on their elbow in front of customers during business hours.