What is the condition under which a limit order will be filled?

A limit order is specifically designed to execute at a price that is specified by the investor, ensuring that they do not pay more than the limit price they set when buying, or sell for less than that limit when selling. Therefore, a buy limit order will only be filled at the stated limit price or lower. This means that the investor is indicating that they want to purchase a security but only if the price falls to their set limit, which protects them from paying more than they are willing to.

Conversely, a sell limit order is intended to execute only at the specified limit price or higher, allowing the seller to ensure that they receive a certain minimum price for their shares. This order type allows investors to have more control over their transaction prices, hence maximizing their purchasing power or potential selling gains.

The other options do not accurately reflect how limit orders function in the market. Limit orders can indeed be filled during regular trading hours, not just after the market closes, and they are not guaranteed to never be filled—proper market conditions simply need to be in place.