Plain English Meaning
A short, strong burst of wind that comes on quickly, gets noticeably stronger than the surrounding wind, and lasts at least a minute before easing off.
Full Definition
A squall is a sudden, sharp increase in wind speed of at least 16 knots, with the sustained speed reaching 22 knots or more, lasting for at least one minute. In a METAR, SQ is the contraction used to report squalls in the present weather group.
Context Anchor
Seen in METAR present-weather codes when an airport weather report is describing sudden strong wind changes.
Derivation
From an old Scandinavian word meaning a sudden gust or roar of wind. The original sense — a brief, violent burst of wind — is exactly how the term is still used in aviation weather today.
Why Pilots Care
Squalls produce rapid that can affect during , , and -.