What It Means
Quantity freeze is the maximum number of shares or contracts a single order is allowed to specify on an exchange. It exists to prevent erroneous "fat-finger" trades — a typo that turns an intended 100-share order into a 100,000-share one — from disrupting the market.
How It Works
Exchanges set the quantity freeze limit per stock or per F&O contract, and it's reviewed periodically as lot sizes and prices change. If you try to place an order above the freeze limit, the exchange simply rejects it — your broker's terminal will usually flag the error before it even reaches the exchange. To trade a genuinely large quantity, you'd need to split it into multiple orders within the freeze limit, which is exactly the friction the rule is designed to create for unusually large single trades.