unidentified flying object

noun

plural unidentified flying objects

: a mysterious flying object in the sky that is sometimes assumed to be a spaceship from another planet

The Peking Evening News said today that it was swamped with telephone calls from people reporting an "unidentified flying object" over the city. The bright round object spotted yesterday turned out to be a research balloon reflecting the sunlight, the newspaper said.

—The New York Times

called also UFO

Word History

First Known Use

1947, in the meaning defined above