Plain English Meaning
At this airport, you cannot ask for a Special VFR clearance to fly in or out when the weather is below normal VFR limits. If the weather is too low for regular VFR, you have to either wait for it to improve or use an instrument flight plan.
Full Definition
A notation on aeronautical charts and in airport directories indicating that fixed-wing Special VFR operations are prohibited within the Class B, Class C, Class D, or Class E surface area at that airport. Special VFR clearances allow flight in below VFR ; a NO SVFR designation removes that for , typically because the airport's or complexity makes such clearances unsafe.