UFO
Unidentified Flying Object — the older, original term for anomalous aerial phenomena, in U.S. government usage from approximately 1952 until replacement by 'UAP' in 2021.
Unidentified Flying Object (UFO) is the historical U.S. government and cultural term for an aerial object that observers cannot immediately identify. Coined by U.S. Air Force Capt. Edward J. Ruppelt in approximately 1952 — Ruppelt was the head of Project Blue Book at the time — the term was intended as a neutral replacement for the press-coined “flying saucer” (which had emerged from the Kenneth Arnold sighting of 1947, Case #00001).
Original definition
Ruppelt’s working definition was specifically operational: a UFO was an object whose identity could not be determined by trained observers. The term carried no implication of origin — extraterrestrial or otherwise. A weather balloon misidentified by an experienced pilot was, by definition, a UFO until correctly identified, after which it ceased to be one.
Cultural drift
Over the subsequent decades, popular usage of “UFO” drifted from Ruppelt’s neutral operational meaning to a near-synonym for “alien spacecraft” — a usage Ruppelt himself would have rejected. This drift is the primary reason for the 2021 transition to UAP.
Current status
The term remains in active use:
- In historical references (Project Blue Book, Roswell, Phoenix Lights, etc.) where the cases predate the UAP rebrand.
- In international contexts (the Brazilian “Night of the UFOs” — Case #00114 — is named in Portuguese with the equivalent term).
- In popular discourse where the cultural connotation is what is intended.
- In MUFON and CUFOS organizational naming, which retain the older term.
Council usage
The Council uses UFO when historical accuracy or cultural precision requires it. Modern cases default to UAP. The two terms are not synonymous in connotation but refer to the same empirical phenomenon: aerial (or, for UAP, all-domain) objects without an immediately determined identity.