Definition
A NOTAM contraction indicating that something — typically the sky, a runway, terrain, or a navigational feature — is hidden from view by clouds, fog, smoke, dust, precipitation, or other surface-based phenomena. When used in sky condition reports, OBSC means the sky is fully hidden by surface-based obscuration rather than by a defined cloud layer aloft.
Plain English
Hidden from sight. The thing is still there, but you can't see it because something — usually weather — is in the way.
Context Anchor
Seen in NOTAMs, airport condition reports, and weather descriptions when a runway feature, light, marking, mountain, tower, or other item cannot be seen clearly.
Derivation
From the Latin obscurare, meaning 'to darken' or 'to cover.' The aviation use keeps that core idea: something is covered up so you can't see it clearly.
Why Pilots Care
Obscured conditions can prevent visual navigation and force reliance on instruments or delay flights.
Intuition Check
Obscured does not always mean completely invisible. In aviation, it can also mean partly hidden or hard enough to see that it may not be reliable.
Example Sentence 1
The NOTAM listed the mountain peak as OBSC due to dense fog along the ridge.
Example Sentence 2
Due to OBSC conditions from haze, the pilot switched to an instrument flight plan.