FIR
Flight Information Region – includes the airspace within specified borders, vertical extent is in general unlimited, except when limited by a UIR. FIRs shall be contiguous to each other. FIS and alerting service are provided in FIR.
UIR
Upper Flight Information Region – established when desirable to limit the number of FIRs through which high flying aircraft have to pass. An UIR always has a specified lower limit.
FIS
Flight Information Service – is provided to give advice and information useful for the safe and efficient conduct of flights. FIS is given to all known aircraft operating or about to operate in a FIR. FIS includes information on SIGMET, serviceability of navigation aids, condition of aerodromes and associated facilities and other information considered pertinent to safety.