Which of the following is NOT a main type of order in trading?

In trading, the primary types of orders that traders use to buy or sell securities are market orders, limit orders, and stop-limit orders.

A market order is a request to buy or sell a security immediately at the current market price, while a limit order sets a specific price at which the trader is willing to buy or sell, ensuring they do not execute the trade at a less favorable price. A stop-limit order combines aspects of both; it becomes a limit order once a specified stop price is reached, giving traders more control over execution prices.

The term "interest rate order" does not represent a recognized or standard type of order in trading. Instead, it might refer to strategies or instruments related to interest rates, such as derivatives or fixed-income securities, but it does not fit into the main categories of orders that traders utilize when executing trades on a trading platform. Thus, this distinction makes it clear why the correct answer is the "interest rate order."