Special VFR is an allowance for a pilot to operate below the standard visibility and cloud clearance requirements for the purpose of getting into or out of an airport in marginal weather conditions.

Obtaining a clearance from air traffic control to operate under special VFR reduces the weather minimums to 1 statute mile and clear of clouds. However, if the special VFR flight is to be conducted at night or during twilight (between sunset and sunrise), the pilot must be instrument rated and the airplane used must be equipped for instrument flight.

ยง 91.157 Special VFR weather minimums.