Which of the following best describes a market order?

A market order is defined as an instruction to execute a purchase or sale of a security immediately at the current market price. This means that when an investor places a market order, they are willing to accept the current prevailing price for that security, which ensures a quick execution of the order. Market orders are typically used when the priority is getting into or out of a position quickly, rather than getting a specific price.

The other options describe different types of orders or trading strategies that do not align with the definition of a market order. For instance, an order to buy or sell a stock at a specified price would be more accurately described as a limit order, which requires the execution to occur only at the designated price or better. An order that combines various types of securities might refer to a portfolio order or a block order, which does not pertain specifically to the immediate execution characteristic of a market order. Lastly, a request to trade stocks at a future date indicates a forward or deferred order rather than a market order, which is executed without delay. Thus, the definition of a market order aligns precisely with the description of placing an order to execute at the current market price.