To shut or close something up (doors, windows, a room), often so that the space is sealed or entry/exit is stopped.
寒いので窓を締め切った。
Because it's cold, I shut the windows.
換気のために一度窓を開けてから、また閉め切ってください。
For ventilation, open the windows once and then close them up again.
大会場を閉め切って発表が始まった。
They closed off the auditorium and the presentation began.
To close or cut off (applications, subscriptions, etc.); to set a deadline after which no more submissions are accepted.
応募の締め切りは来週の金曜日です。
The application deadline is next Friday.
定員に達したので、申込みを締め切った。
We reached capacity, so we closed applications.
購読の受付を締め切る前に説明会を開く予定だ。
We plan to hold an info session before we close subscriptions.