An air show was an event involving airplanes and aerial objects performing for the amusement of an audience. Air shows usually had special planes flying complex patterns.
When Enterprise NX-01 went back in time to 1944 in an effort to stop the Na'kuhl, a shuttlepod from Enterprise encountered a group of planes which Travis Mayweather recognized as P-51 Mustangs. Travis also told Commander Charles Tucker III that he had seen that class of plane at air shows. Tucker replied that he didn't believe the P-51s they were seeing to be part of an air show. (ENT: "Storm Front")