UFO

A UFO, or unidentified flying object, is any observed airborne object or phenomenon that cannot be readily identified by the observer. The term does not imply the object is extraterrestrial; most UFO sightings are later identified as conventional aircraft, balloons, meteorological phenomena, or optical effects.

The term "UFO" entered popular usage after World War II, with the 1947 sighting by pilot Kenneth Arnold and the 1947-1950 surge of reports of "flying saucers." In recent years, many official agencies prefer the term UAP, or unidentified aerial phenomena, to avoid stigma and emphasize research questions.

Investigation: In the United States, Project Blue Book (1952–1969) investigated thousands of reports; the majority were explained, with only a small fraction unresolved. Similar programs exist or existed in other countries. Government and military agencies have published occasional assessments, noting that most UAP reports remain poorly understood due to limited data.

Recent developments: In 2021, a U.S. Defense Intelligence Agency and Office of the Director of National Intelligence assessment summarized a large number of reports from 2004–2021, stating that most could be explained by conventional causes or lacked sufficient data, while a subset displayed unusual flight characteristics but did not provide evidence of propulsion or origin.

Interpretation and research: The field includes government, military, scientific, and civilian researchers. There is ongoing debate about origins, with explanations ranging from misidentifications to atmospheric phenomena, drones, or classified technology. No definitive evidence has established an extraterrestrial origin for any UAP to date.