Definition
A NOTAM contraction indicating that a runway, taxiway, airport, airspace, navigation aid, or other facility is not available for use during the stated period. When something is published as CLSD, pilots may not operate on or use it until the closure is lifted.
Plain English
Shorthand used in NOTAMs and other aviation notices to say that a runway, taxiway, airport, or facility is shut and cannot be used right now.
Context Anchor
Seen in aviation notices and airport information for runways, taxiways, airports, ramps, and services that are temporarily unavailable.
Derivation
A standard aviation contraction of the everyday word 'closed,' shortened to four letters so it fits within the compact, telegraphic format used in NOTAMs and other operational notices.
Why Pilots Care
Pilots must confirm operational status to avoid attempting to land or taxi on a closed surface, which creates immediate safety and regulatory violations.
Intuition Check
Closed does not mean “use with caution.” It means “do not use” unless you have clear authorization that changes the situation.
Example Sentence 1
The NOTAM read 'RWY 09/27 CLSD,' so we planned to use Runway 18 for departure.
Example Sentence 2
A NOTAM stated the airport would be CLSD overnight due to snow removal.