In the process of preparing; often used on signs to mean a shop or facility is not yet open for business.
入口の看板に『準備中』と書いてあったので、また後で来ます。
The sign at the entrance said '準備中', so I'll come back later.
イベントは準備中のため、入場できません。
The event is in preparation, so admission is not allowed.
システムが準備中です。完了までしばらくお待ちください。
The system is being prepared. Please wait a moment until it's ready.
厨房は今準備中なので、料理はまだ出せません。
The kitchen is currently preparing, so we can't serve dishes yet.