IFR is the abbreviation for Instrument Flight Rules. These are in place to provide guidelines and regulations for safety of filght in low visibility conditions using the instrument panel and navagation radios as the main reference for flight. Special rules apply to IFR flight as opposed to flight during VFR conditions. Such rules include the amount of fuel required to be onboard the aircraft. Visibility conditions, enroute navagation, communications, flight planning, and landing approaches are all covered in the FAR's. Regulations concerning IFR flight can be found specifically in parts 91 and 95.
rating requires further training after the private pilot
certification to allow pilots to fly in bad weather. A pilot needs to be trained to not merely fly by instruments alone, but also to understand the Air Traffic Control
system. IFR flight is continuously monitored by ATC