Instrument Flight Rules- A type of flight operation that allows the pilot to fly solely by reference to his/her instrument panel. No outside visual cues are needed. This type of flying is required when weather conditions such as low visibility or clouds obscure the pilot's reference to the horizon, and requires a flight plan and Air Traffic Control (ATC) clearance. An Instrument Rating is required to fly under IFR.
Visual Flight Rules- A type of flight operation that requires the pilot to be able to see outside of the airplane and use visual cues to control the aircraft. This is the basic type of flying that student pilots learn before being able to fly under IFR, as not seeing outside can disorient the pilot and make it very difficult to fly without proper training.