Plain English Meaning
A special permission from air traffic control to fly visually in or out of an airport's controlled airspace when the weather is too poor for normal visual flying, as long as you can stay clear of clouds and see at least one mile.
Full Definition
An ATC authorization that allows a pilot to operate under visual flight rules within the surface area of controlled airspace when the weather is below standard VFR minimums. Special VFR generally requires at least 1 statute mile flight visibility and the ability to remain clear of clouds, and it must be specifically requested from and approved by ATC. At , and must each be .