1To close or shut something (e.g. a door or window), making it not open; can also imply fastening/locking in some contexts.
母が出かける前に窓を閉めてくれた。
My mother closed the window before leaving.
寒いので、窓を少し閉めてください。
It's cold, so please close the window a little.
帰るときは必ず戸を閉めて鍵をかけてください。
When you leave, always close the door and lock it.
冷房が効きすぎるからドアを閉めておいてください。
The air conditioning is too strong, so please keep the door closed.