An NACA duct is a distinctive style of low-drag air intake. It takes its name from the National Advisory Committee for Aeronautics, a U.S. government agency founded in 1915 to... well... advise on aeronautics. (NACA evolved into NASA, the National Aeronautics and Space Administration, in 1958.) Although originally developed for aircraft, NACA ducts have appeared on a number of automobiles and motorcycles designed in the 1970s and 1980s. Notable examples of NACA-duct-equipped cars include the Ferrari F40 and Lamborghini Countach. Some of these ducts were functional air intakes, but others were merely cosmetic--meant to convey an impression that the vehicles were high-tech and high-performance, like jet aircraft.
As an aside, "NACA" is an initialism, not an acronym (that is, the letters are pronounced individually, not as a single word).
