Which of the following best describes a 'stop-loss order'?

A stop-loss order is best described as an order to sell a security to prevent further losses. This type of order is used by investors who want to limit their losses on a position by automatically triggering a sale if the security reaches a certain price, thereby helping to mitigate the impact of a declining market. The primary purpose of a stop-loss order is to provide a safety net for investors, ensuring that they do not hold onto a losing position indefinitely and thereby protecting their capital.

The other options represent different concepts in trading. An instruction to buy a security at a specified lower price relates more closely to a limit order, which is not the same as a stop-loss. The manual process of tracking securities doesn't align with the nature of a stop-loss order, as that involves active monitoring but not automatic execution, and an investment strategy to maximize gains refers to techniques aimed at increasing profits, which is distinct from loss prevention strategies like stop-loss orders.