Just what UFO?
A UFO is colloquial with an Unidentified Flying Object. Often, in popular culture, they are defined as Alien Spacecraft, however, entirely technicality, anything can be a UFO, provided that it seems being flying under its own power and also you cannot identify it.
A broad portion of UFOs reported actually turn out to be common stuff like a weather balloons and atmospheric lights. However, at that time them to be unidentified, the nomenclature 'UFO' was appropriate until its true nature was discovered.
However, there remains a substantial part of UFOs that remain 'Unexplained', it's from these, that often we obtain our concept that the item is definitely of Alien Origin. However, one can argue, that as a result of cultural bias the UFO culture, that anybody seeing an object they can not identify it, will identify it subconsciously being an Alien Spacecraft; until its nature is revealed. This stands out when considered, that individuals can't see unidentified objects in the more mundane view, and possibly, is an example whereby the expectations dictate the outcome.
And while seemingly, lots of people might think this phenomenon is of no importance, it ought to be noted that the Government has thought it important enough to have three different examinations about the matter, with the length of our history. The initial was the 'Flying Disc File'; that was the FBI's investigative focus on the phenomenon of flying saucers. Then there was Project Sign; that was a similar project, conducted by the Air Force. Lastly, there was Project Blue Book, a bigger Air Force Program, that seemingly consolidated all past reports.