A flypast is when planes, often military ones, fly over a place on a special day so people can watch — a national holiday, a royal birthday, the end of an air show. The planes may fly in a shape, or in a line, quite low, then they are gone. It is a show, and often a ceremony. This is mainly British English. In American English the usual word is flyover. You would not use flypast for a random plane going over your house. It is a public, planned flight for an audience. Though actually, one plane can do a flypast, but the picture in most people’s minds is a group. And this is not a space flyby: nobody is gathering science from a planet. The planes are there to be seen.

空中分列（英式；戰機飛過給人看。台灣國慶常說「衝場」；美式多說 flyover）