Definition
Weather conditions in which visual flight is still legally permitted, but visibility and cloud ceilings are reduced to the lower end of the Visual Flight Rules range — specifically, a ceiling of 1,000 to 3,000 feet and/or visibility of 3 to 5 statute miles. These conditions are abbreviated MVFR on weather products.
Plain English
Weather that is just barely good enough to fly by looking outside. The clouds are low and the air is hazy, so a pilot can legally fly visually but has very little room for error.
Context Anchor
You will see this term when checking weather reports, forecasts, or training scenarios before deciding whether a VFR flight is a good idea.
Derivation
Marginal comes from the Latin marginalis, meaning 'on the edge.' Here it means the weather is on the edge of acceptable for visual flight — better and it would be plain VFR; worse and it would be IFR.
Why Pilots Care
Signals the need for extra caution, possible instrument backup, or route changes as conditions can quickly drop below VFR limits.
Grounding Statement
Picture flying under a low cloud layer with only a few miles of view ahead; the flight may still be VFR, but the safe choices become much tighter.
Intuition Check
Marginal does not mean automatically illegal or impossible. It means the weather is still in the VFR category, but close enough to the lower limits that a pilot should treat it with extra caution.
Example Sentence 1
The morning briefing showed marginal VFR conditions along the route, with a 1,500-foot ceiling and four miles visibility in haze.
Example Sentence 2
With marginal VFR conditions forecast along the route, the instructor added extra fuel and checked nearby instrument approaches.