Plain English Meaning
The lowest visibility a commercial operator is allowed to have at the airport before they can legally take off when the weather is poor. Smaller aircraft generally need at least one mile of visibility; larger aircraft with three or more engines can go with half a mile.
Full Definition
The minimum visibility (and sometimes ceiling) values a pilot operating under Part 121, 125, 129, or 135 must have at the departure airport before commencing an instrument flight rules takeoff. Standard values are 1 statute mile visibility for aircraft with two engines or fewer, and 1/2 statute mile visibility for aircraft with more than two engines, unless higher minimums are specifically published for that airport.
Context Anchor
Seen when reviewing a Standard Instrument Departure, information, or the airport’s published departure notes before an .