What is a "Limit Top" order?
Limit Top order are for users who want: (1) To avoid paying higher take fees, (2) To trade at the best market price, and (3) Quick order entry. A Limit Top order will be sent at a price equal to the best price in the order book at that time. Unlike standard limit orders, no price input is required from the user. For example, if you are a buyer, it will enter a limit order at the best bid in the order book and place it in the order book. The order will remain there in-line with your Time-In-Force (TIF) selection or until executed.
Check out this blog post for more information!