IOC
Immediate-or-Cancel — an order that fills whatever quantity is available at the limit price right now and cancels the remainder.
Definition
An Immediate-or-Cancel (IOC) order attempts to fill as much of the requested size as available at the specified limit price and cancels any unfilled portion instantly. Unlike FOK, IOC accepts partial fills. Unlike GTC, nothing rests on the book after the sweep.
In practice
IOC is useful when a bot wants to take available liquidity without risking a partial GTC sitting exposed. For example, a bot sending an IOC for 200 YES shares at $0.56 might receive only 130 shares if that is all the book offers at or below $0.56. The remaining 70 shares are cancelled. The bot then decides whether to chase the remaining size or wait for the next signal cycle. IOC is less common on Polymarket than FOK, but it is useful in thin markets where full fills are unlikely.