If something happens 24-7, it happens all the time: twenty-four hours a day, seven days a week. A shop, a hotline, or a factory is 24-7 when it never shuts. People also stretch it. “She’s on her phone 24-7” usually means “far too much”, not that she never sleeps. It is informal spoken and written English; you will also see 24/7. Kind people save the strong wording for things that really do not stop, and use “all the time” when they are only annoyed.

全天候；二十四小時、一週七天都在。台灣店家招牌更常寫「24小時營業」或「全年無休」，較少寫 24-7。