Outside air temperature
In aviation terminology, the outside air temperature (OAT) or static air temperature (SAT) refers to the temperature of the air around an aircraft, but unaffected by the passage of the aircraft through it.
Aviation usage 
The outside air temperature is used in many calculations pertaining to flight planning, some of them being takeoff performance, density altitude, cruise performance and go-around performance. In most texts, the abbreviation, "OAT" is used.
Most performance and flight planning graphs and tables use either degrees Celsius or Fahrenheit or both. The Kelvin scale, however, is used for Mach number calculations. For example, the speed of sound in dry air is
Outside air temperature can be obtained from the aviation meteorological services, on the ATIS or measured by a probe on the aircraft. When measured by the airplane's probe in flight, it may have to be corrected for adiabatic (ram effect) rise and friction, particularly in high performance aircraft.
See also 
- Ground Studies for Pilots: Flight Planning, Sixth Edition (Ground Studies for Pilots Series), Peter J. Swatton, Wiley-Blackwell; 6 edition (December 3, 2002), 978-0632059393