No.
UFO simply stands for Unidentified Flying Object. Which could refer to anything you do not recognise. A weather balloon, an airplane, a frisby. None of which are known to use plasma.
It could be. So long as it's unidentified to the observer it's a UFO. In fact, to extremely secluded cultures, helicopters and planes are UFOs.
using UFOS
The term UFO stands for Unidentified Flying Object. If it's an unknown there is absolutely no way tell what kind of fuel it takes.
Personally, I ponder dubiously evidence of UFOs.
Personally, I ponder dubiously evidence on UFOs.
By unconvential propulsion such as a gravity beam (using microwaves) or maybe using electrogravitics.
Where humans and alcohol are, UFOs will be.
There have been reports of sightings of white UFOs.
the correct answer is UFOs thanks for asking
The ones who study UFOs are called Ufologist. They study every thing about unidentified flying objects (UFOs).
The most common UFOs to be reported are not crafts, but balls of light or BOLs. This really depends on the conditions upon seeing this BOL. An aircraft could take on that appearance if given substantial conditions.
UFOs can go as high as your imagination allows.