Well, put simply, they are the mythical flying "chariots" out of the South Asian epics. Though, interestingly enough, the earliest mentions of them specifically exclude mentions of horses//being horse drawn.
They are entirely self moving. The word means to traverse, traverse/measure out.
In the ancient epics, they were as large as some palaces, and sometimes listed as a palace (for a character in the epics) and interesting is the evolution of the word today from the days of the epics to where it now means airship/craft.
In the Ramayama, the character and villain, Ravana (inspiration for Rahvin for you WoT fans), has a vimana described as: resembling the Sun, and a chariot able to traverse anywhere and everywhere, resembling a bright cloud, and by command, could go into the atmosphere.
Vimana can travel the skies at insane speed, and notably rain down fire and weapons of mass destruction in battles. Idk about you, but that sounds like some space ship level stuff.
Maybe Stargate was onto something. :SG1 MUSIC INTENSIFIES:
Viman can be shaped into many ways, however. One story tells of a flowery Viman shaped like an eagle that Lord Vishnu sent down to carry the soul of one person up to heaven. Important to also note that Eagles are important in the mythos as they are associated with Garuda a deity and divine bird being who is eagle-like (like not 1-1), as well as often related to a kite (the bird) and yes, the toy that flies through the air is derived in name from the bird. Anyways, Garuda is the mount of Lord Vishnu, and so through him eagles also have a level of high prominence - another example is Shyena, the divine eagle associated with Agni (god of fire).
Anyways circling back to Vimana, some could go invisible (cloaking engaged). But, yeah, read the South Asian epics and myths, there is mind blowingly cool stuff in them.