The term "Close Encounter" was coined by astronomer and writer J. Allen Hynek in his 1972 book "The UFO Experience: A Scientific Inquiry." Hynek, a renowned expert in the field of UFO (Unidentified Flying Object) studies, developed a classification system to categorize various types of encounters between humans and unidentified aerial phenomena. The system consists of five levels, ranging from a distant sighting to a physical encounter with an extraterrestrial being.