Special VFR (Visual Flight Rules) allows aircraft to fly in weather conditions in which such flight would normally be prohibited. VFR flight is prohibited when visibility is poor or aircraft cannot remain sufficiently far away from clouds because of the risk of collision with other aircraft. In areas where there is air traffic control and low use, this problem can be averted by simply allowing only one aircraft through the area at a time.
Because of the increased risk, controllers are generally prohibited from offering special VFR - a pilot specifically requests it. Controllers have been known to hint at it when a pilot has no other option by saying things like "is there anything special you might want"?
