Margin call
A margin call is the exchange's warning that a leveraged position is close to liquidation: its losses have used up most of the margin, and you need to add margin or reduce the position.
On Binance futures, the margin ratio is the maintenance margin divided by your margin balance. At 100% the position is liquidated; Binance recommends keeping the ratio below 80% and sends margin call and liquidation call notices by email and in-app message. It does not promise they arrive in time, and in a fast move it may skip the margin call and send only the liquidation notice. Treat a margin call as a sign the trade went wrong, not as a reason to add money: your stop should have closed it before the call came.
Learn more: how to avoid liquidation and what margin is.