The Difference Between UFOs and UAPs

Term: UFO: unidentified flying object, an object seen in the sky that the witness cannot identify.

Term: UAP: unidentified anomalous phenomena, the term U.S. law and the Pentagon now use for unidentified airborne, transmedium, and certain submerged objects.

Term: Transmedium: able to move between environments, such as between the atmosphere and the ocean, or between space and the atmosphere.

Term: AARO: the All-domain Anomaly Resolution Office, the Pentagon office that collects and analyzes UAP reports.

The Difference Between UFOs and UAPs

UFO stands for unidentified flying object. UAP stands for unidentified anomalous phenomena. Both terms describe something people cannot identify. UAP is the newer, broader term. It is the wording used in federal law, and it covers objects that move between air and water or space, and objects underwater, as well as objects in the sky. Neither term means alien spacecraft.

UFO vs UAP at a glance

Stands for: UFO means unidentified flying object. UAP means unidentified anomalous phenomena.

Origin: UFO was created by Air Force Captain Edward Ruppelt in the early 1950s to replace “flying saucer.” UAP was used by the Pentagon from 2020 as “unidentified aerial phenomena,” and changed to “anomalous” in December 2022.

Scope: UFO covers objects seen flying. UAP covers airborne objects, transmedium objects, and certain submerged objects.

Where you see it: UFO appears in popular use, Project Blue Book records, and older reports. UAP appears in federal law, AARO and NASA documents, and current congressional hearings.

Where the word UFO came from

Pilot Kenneth Arnold reported nine fast objects near Mount Rainier in June 1947. The press called them flying saucers, and the name stuck. The Air Force studied these reports under Project Sign, Project Grudge, and then Project Blue Book, which began in March 1952.

Captain Edward Ruppelt ran Blue Book in its early years. In his 1956 book, he wrote that UFO was the official term he created to replace flying saucers. The military wanted a word that did not assume a saucer shape or an alien source. Blue Book ended in December 1969, and the term UFO stayed in popular culture.

Why the government moved to UAP

By the 2000s the word UFO carried a stigma. A 2021 intelligence assessment said sociocultural stigma was an obstacle to collecting data, and that no standard reporting system existed for pilots until the Navy created one in March 2019. Officials wanted a term that sounded like data collection and not like science fiction.

In August 2020 the Pentagon created the UAP Task Force, using the wording unidentified aerial phenomena. In December 2022, the fiscal year 2023 defense bill changed the word aerial to anomalous. Under Secretary of Defense Ronald Moultrie told reporters that the new wording expands the scope to include submerged and transmedium objects.

Federal law now defines unidentified anomalous phenomena in three parts. The first is airborne objects that are not immediately identifiable. The second is transmedium objects or devices. The third is submerged objects or devices that are not immediately identifiable and that behave in ways suggesting a link to the airborne objects. The law is 50 U.S.C. 3373. NASA follows the same wording.

What neither term means

The word unidentified means not yet identified. It does not mean alien, and it does not mean spiritual. The label covers a wide mix. Pentagon investigators report that most UAP cases they resolve turn out to be balloons, birds, satellites, aircraft, and drones. In its 2025 annual report, AARO resolved 114 of 319 new reports and attributed them to those objects, plus one rocket launch and one person using a jet pack.

The label also covers cases that remain unresolved. AARO said in the same report that a lack of timely sensor data continues to limit its ability to resolve cases. Unresolved means the data cannot support a conclusion. It does not mean the object was proven to be anything in particular.

One more point about wording. Older books, websites, and even some current ones still expand UAP as unidentified aerial phenomena. That was the official wording until December 2022. If you see it, you are reading the older definition.

Which term should you use?

Use UFO when you talk about the popular subject or the historical record before 2020. Use UAP when you cite current government reports, hearings, or law. In my own writing I use both, and I keep in mind that neither word tells you what these objects are.

That question is the one my book Disclosure: They Are Not Extraterrestrials takes up. It looks at the evidence for what is behind the reports, from ancient records to the Pentagon files released in 2026. Disclosure is available on Amazon. You can find more of my work at ckqbooks.com.

Sources

50 U.S.C. 3373 (definition of unidentified anomalous phenomena). Edward J. Ruppelt, The Report on Unidentified Flying Objects (1956). Office of the Director of National Intelligence, Preliminary Assessment: Unidentified Aerial Phenomena (June 25, 2021). DefenseScoop, December 19, 2022, on the Pentagon’s terminology change. NASA UAP FAQ, science.nasa.gov/uap/faqs. AARO Fiscal Year 2025 Consolidated Annual Report on UAP (aaro.mil).