UAP/UFO Glossary
Core Terms
UFO (Unidentified Flying Object)
The traditional term for any airborne object that cannot be identified by the observer. The term gained widespread use after Kenneth Arnold's 1947 sighting. It carries no inherent implication of extraterrestrial origin—a UFO is simply something unidentified.
UAP (Unidentified Anomalous Phenomena)
The current official U.S. government terminology, replacing "UFO" in official contexts. The term was broadened from "Unidentified Aerial Phenomena" to "Unidentified Anomalous Phenomena" to encompass objects observed in multiple domains.
Legal Definition (50 USC 3373):
- (A) airborne objects that are not immediately identifiable;
- (B) transmedium objects or devices; and
- (C) submerged objects or devices that are not immediately identifiable and that display behavior or performance characteristics suggesting that the objects or devices may be related to the objects described in subparagraph (A).
IFO (Identified Flying Object)
A UFO that has been explained. When investigators determine a sighting was caused by a satellite, aircraft, planet, or other mundane source, the UFO becomes an IFO.
Official Classification Terms
Transmedium
Objects or devices observed to transition between different physical domains—specifically, between space and the atmosphere, or between the atmosphere and bodies of water. The term defines a reporting category in official usage; it does not confirm that such objects possess advanced technology.
NHI (Non-Human Intelligence)
A term used in recent legislation and hearings to refer to hypothetical intelligent entities that are not human. The term is intentionally neutral, avoiding assumptions about whether such intelligence would be extraterrestrial, interdimensional, or of another origin.
Technologies of Unknown Origin
A term from UAP legislation referring to materials or devices that cannot be attributed to known human manufacturing. Like other official terms, its presence in law creates a reporting category rather than confirming such technologies exist.
Hynek Classification System
Developed by Dr. J. Allen Hynek and published in The UFO Experience: A Scientific Inquiry (1972), this system categorizes UFO sightings by type and proximity.
Distant Sightings
Nocturnal Lights (NL)
Anomalous lights observed in the night sky. The most common category, but also the most difficult to investigate due to limited detail.
Daylight Discs (DD)
UFOs observed during daytime, typically described as disc-shaped or oval. Daytime sightings allow for more detail but are less common.
Radar-Visual (RV)
Cases where UFOs are detected on radar simultaneously with visual observation. These cases were considered higher-value evidence due to instrumental confirmation.
Close Encounters
Encounters occurring within approximately 500 feet (150 meters) of the witness.
Close Encounter of the First Kind (CE1)
A close visual sighting of a UFO showing appreciable detail, but with no physical interaction with the environment or the witness.
Close Encounter of the Second Kind (CE2)
A close encounter that produces physical effects, such as:
- Ground marks or impressions
- Burned or affected vegetation
- Chemical traces
- Electromagnetic interference (vehicle stalling, radio static)
- Physiological effects on witnesses (heat, paralysis, discomfort)
- Animal reactions
Close Encounter of the Third Kind (CE3)
A close encounter in which occupants or entities are observed in or near the UFO. Hynek distinguished this from "contactee" claims, which he generally excluded from scientific consideration.
Later Additions (Not from Hynek)
Other researchers have proposed additional categories, though these lack universal acceptance:
Close Encounter of the Fourth Kind (CE4)
Proposed to describe cases involving abduction—where a witness claims to have been taken aboard a craft. Not part of Hynek's original system.
Close Encounter of the Fifth Kind (CE5)
Proposed by Steven Greer to describe cases of allegedly initiated human-to-entity contact. Controversial and not widely accepted in mainstream ufology.
Government Programs and Offices
AARO (All-domain Anomaly Resolution Office)
The current Pentagon office responsible for investigating UAP reports, established July 2022. Replaced the UAPTF.
AATIP (Advanced Aerospace Threat Identification Program)
Pentagon program (2007-2012) that investigated unidentified aerial phenomena. Its existence was revealed publicly in December 2017.
UAPTF (Unidentified Aerial Phenomena Task Force)
Pentagon task force (2020-2022) that preceded AARO. Produced the preliminary assessment delivered to Congress in June 2021.
Project Blue Book
U.S. Air Force UFO investigation program (1952-1969). Investigated 12,618 sightings; 701 remained unexplained.
Research Organizations
NUFORC (National UFO Reporting Center)
Civilian organization that has collected UFO reports from the public for over 50 years. Maintains a public database of sightings.
MUFON (Mutual UFO Network)
World's oldest and largest civilian UFO investigation organization. Uses trained field investigators to examine reports.
CUFOS (Center for UFO Studies)
Scientific organization founded by J. Allen Hynek in 1973 to promote serious study of UFO reports.
Observable Characteristics
Terms used in official reports to describe reported UAP behavior:
Five Observables
A framework sometimes used to describe anomalous UAP characteristics:
- Anti-gravity lift: Apparent ability to hover or maneuver without conventional lift mechanisms
- Sudden and instantaneous acceleration: Movement without apparent inertia
- Hypersonic velocities without signatures: Extreme speeds without sonic booms or visible exhaust
- Low observability (cloaking): Ability to be undetectable to certain sensors
- Trans-medium travel: Movement between air, water, and space
Other Terms
FLIR (Forward Looking Infrared)
Thermal imaging technology used on military aircraft. Several famous UAP videos (FLIR1/Tic Tac, GIMBAL, GO FAST) were captured using FLIR systems.
Tic Tac
Informal name for the object observed during the 2004 USS Nimitz encounter, based on Commander David Fravor's description of its shape as resembling the breath mint.
GIMBAL
One of three Navy UAP videos officially released by the Pentagon in April 2020. Shows a rotating object captured on FLIR in 2015.
GO FAST
One of three Navy UAP videos officially released by the Pentagon in April 2020. Shows a rapidly moving object captured on FLIR in 2015.
Foo Fighters
Term used by World War II pilots for mysterious aerial phenomena encountered during combat missions. Origin of later UFO interest.
Flying Saucer
Popular term originating from press coverage of Kenneth Arnold's 1947 sighting. Arnold described the objects' movement as being "like a saucer skipped across water," which reporters transformed into a description of the objects' shape.