Auras are mostly incorporeal but lasting manifestations of elemental power. They usually affect a 2x2 area and can be cast anywhere in the realm. Entangle Terrain is an example of an aura. Auras have characteristics, specifically aura characteristics, and are one of the six card types in the game. The 'Casting Auras' entry has details on how to cast aura spells.
Some effects can move an aura by force (e.g. Windblast) and some auras can move themselves (e.g. Thunderstorm). Auras ignore the regional boundary between the surface and void when moving. (Wildfire's 'adjacent locations' are still defined by its current region.) For example, a Thunderstorm moves itself with its end-of-turn ability. It can take a step into the void with this movement, though not to the subsurface. Additionally, an aura being moved by force (e.g. Displace or Windblast) can be moved from surface locations to void locations, and visa versa. This only applies to non-minion auras. See 'Cards with Multiple Types' for details on Aura Minions.