Unidentified flying object

UFO landing strip in Cachi, Argentina

A UFO (Unidentified Flying Object) is any object flying in the sky which cannot be identified by the person who sees it. Sometimes the object is investigated. If people can still not figure out what the object is after an investigation, it is called a UFO. If they figure out what the object is, it can no longer be called a UFO because it has been identified.

UFO, Jakobsdal, Linköping, Sweden

Even though UFOs might have different origins, people often use the word UFO when they are talking about alien spacecraft. Flying saucer is another word that is often used to describe an unidentified flying object. Some UFOs that are seen in the water, or going in or out of the water are called USOs (Unidentified Submerged Objects).

Identified flying objects (IFOs)

Studies estimate that 50-90% of all reported UFO sightings are identified later. Usually 10-20% are never identified. Studies also show that very few UFO sightings are hoaxes (people trying to trick other people). Most UFOs are actually natural or man-made objects that looked strange.

80-90% of IFOs are identified as one of three different things:

astronomical causes (for example: planets, stars, or meteors)
aircraft
balloons (including weather balloons)

10-20% of IFOs are other causes (such as birds, clouds, mirages, searchlights, etc.)

Unidentified Flying Object Media

"GIMBAL" Pentagon UFO video, January 2015
An example of picture showing a ship that appears to be floating above the horizon.
SpaceX Falcon 9 Launch from Vandenberg, CA - October 7 2018 - 45131925812
The celestial phenomenon over Basel in 1566.
Cover of the 1953 book The Flying Saucers Are Real by Donald Keyhoe
Cover of the pulp science fiction magazine Amazing Stories from October 1957
A Roswell Daily Record on July 8, 1947, reporting a UFO case
A document about a sighting of a UFO that occurred on December 16, 1977, in the state of Bahia, Brazil
Allen Hynek (left) and Jacques Vallée
UFO drawing, authenticity unknown, attribution and date unspecified. One of hundreds of files resulting from US President Bill Clinton's 1995 order to the CIA to declassify all documents with "historical value" that were at least 25 years old.