Immediate or Cancel order (IOC) is an order type similar to Fill or Kill (FOK) except that it accepts a partial order execution. The remaining part of the order (the part that is not executed instantly) is then cancelled. Fill and Kill (FAK) is another name given to IOC orders.

Pros: Effective option for large volume orders fulfillment (Institutions and Funds). Avoids driving price further than closest price in the order book (versus FOK). 

Cons: Difficulty to control buy/sell price efficiently (or buy at limit). Large orders can fully execute all orders at the opposite side of the order book (triggering liquidity syphoning).

Immediate or Cancel can be used in combination with limit and stop orders (triggering only when a threshold is met and has to execute instantly). The unfilled part, if any, is then cancelled.

IOC pays taker fees.