The Hebrew word for it is Merkabah which is the word used in tradition for the celestial chariot in which Elijah went back to heaven. I've been singing "Jerusalem" all my life and now I think I'm finally getting a handle on what Blake was talking about. "Bring me my chariot of fire" means something like "let me realise my full potential"- only "chariot of fire" sounds better.
We think our consciousness is trapped in our physical bodies but really we're travelling around in an invisible vehicle that would blaze out like the sun if we let it.