What is the difference between day order vs immediate or cancel..??

A "Day Order" duration is valid until the end of the extended trading session.

An "Immediate or Cancel (IOC)" order allows a Trading Member to buy or sell a security as soon as the order is released into the market, in case order failed to full fill the total quantity it will be removed from the market. Partial match is possible for the order, and the unmatched portion of the order is cancelled immediately.