A UFO is an unidentified flying object, but it's almost an impossibility it's alien. (It is possible that an old race had a probe close enough to pick up our radio and over the last hundred years they contacted their home and visited recently, but that is more storytelling than science)
Can't deny the possibility of a new race as well, if you look at the doctor who disappered in China after he came up with some formula for enhancing biology of a child in womb, who knows someone made enhacement to it as well, and make a baby rise 1000 yrs in a week, and he learned physics, chemistry, biology in a day, and is now looking down on us
, from the UFO he made...