To square off is to close an open position. If you bought 100 shares intraday, you square off by selling 100; if you sold short, you square off by buying back. In futures and options, squaring off before expiry is how most traders exit, rather than waiting for settlement. Brokers automatically square off intraday positions that are still open near the close, usually between 3:15 and 3:25 PM for equities, and they charge a fee for doing it. Suppose you bought SBI at ₹800 in an MIS order and forgot about it; at 3:20 PM the broker sells it at the market price, whatever it is. Auto square-off also applies when margin runs short. Squaring off yourself, at a price and time you chose, is always better than letting the broker do it in a rush at the end of the day.