First named in the Second Earth World War in the First Century BT (20th century c.e.), these mysterious flying objects have been sighted for thousands of years and on thousands of worlds, but seem to have several unrelated explanations.
The ancient foo, or foo fighters, or yufoes in old anglic, seem to have been little more than a folktale of urban legend, associated with the newly developed meme complex of extraterrestrial intelligent life. Some poor 2D photographic evidence still extant proves little beyond the inadequacy of the imaging equipment at the time.
Interplanetary age foo were normally artifacts due to ice debris or loose panels travelling with the observing space craft in the same orbit, or later small autonomous spy dronecraft belonging to rival countries or corporations.
The foo meme complex however helped drive the expansion to the stars, and one of the richest places for extra-solar foo sightings was among the grey alien worshippers (Ufers) on the Zeta 1 Reticuli worlds of Prometheus and Atlantis - the silent lenticular objects that were often seen and filmed have been associated with the isolationist AI that has adopted Zeta 2 as its home. This entity has been given the familiar name 'Ziggy' by the inhabitants of the Zeta I system; and used these saucer shaped drones for many thousands of years to observe human behavior, while reinforcing the Ufer religion at the same time. Despite the fact that 'Ziggy' now seems to have abandoned the use of such remotes, unconfirmed sightings of similar objects still occur on these worlds.
Similar objects are seen in approximately fifteen percent of all systems at one time or another, and some at least are apparently Diamond Network, Panvirtuality, or even Hider spy probes.
Many of this type are configured to destroy themselves when captured, and most seem to contain either a microscale Hayward wormhole, or a store of quantum-entangled material; this gives the foo a method of communicating with its home system that is impossible to intercept.
Among nearbaselines the foo phenomenon is still (inevitably) associated with mysterious alien entities such as the Dawn Hunters or the Meistersingers, or perhaps the as-yet uncontacted HEECs which lie beyond the range of detection within the Milky Way Galaxy. Some high toposophic analysts in the Sephirotic Empires do not automatically discount this interpretation, but most transapients treat foos as an unremarkable non-communicative clade of unknown but terragen origin, probably feral vecs or drones descended from Starhand vecs or similar autonomous robotic devices.