IOC stands for Intelligent Orientation Control. It is the F mode on the 3-position switch of the controller. It is currently not active, but with a future firmware upgrade will allow Course Lock, Home Lock and Point of Interest (POI) flight modes that are similar to the Phantom 2 Naza FC flight modes.
IMU stands for Inertial Measurement Unit, which is the sensor that orients the Inspire in 3 dimensional space, and tells the FC, or Flight Controller, what level, unaccelerated flight is, so that when you leave sticks in neutral the Inspire hovers in level flight. An IMU calibration has to be done with the Inspire on a level surface and without any disturbance during calibration. Basically, its a set of accelerometers that sense minute changes in orientation and speed, just like the Big Birds use.