Definition
A temporary physiological condition caused by rapid travel across multiple time zones, in which the body's internal circadian rhythm becomes misaligned with the local time at the destination. Symptoms commonly include fatigue, disturbed sleep, reduced alertness, impaired concentration, headache, and digestive upset, and they typically persist until the body adjusts to the new day-night cycle.
Plain English
The tired, foggy feeling you get after flying across several time zones, because your body's internal clock is still set to where you came from.
Context Anchor
Pilots encounter this term in discussions of long-distance travel, international flying, crew rest, and personal fitness to fly.
Derivation
From 'jet,' referring to jet aircraft that made fast long-distance travel common, and 'lag,' meaning to fall behind. The term emerged in the 1960s when jet travel first allowed people to cross enough time zones quickly enough for the body's internal clock to fall noticeably behind local time.
Why Pilots Care
It can impair alertness, judgment, and reaction time, raising the risk of errors during flight operations and requiring careful crew scheduling and rest planning.
Analogy
It is like arriving at breakfast time while your body still thinks it is the middle of the night.
Intuition Check
Jet lag is not just ordinary travel tiredness. It specifically comes from crossing time zones faster than the body can adjust.
Example Sentence 1
After flying from Los Angeles to London, the crew built in a 24-hour rest period to recover from jet lag before the return leg.
Example Sentence 2
The airline built a 24-hour layover into the roster to reduce the effects of jet lag before the next duty period.