Plain English Meaning

Dehydration is when your body doesn't have enough water to work properly. Heatstroke is when your body gets so hot it can no longer cool itself down. Both are dangerous in flight because they reduce a pilot's ability to think and react.

Full Definition

Two related heat-stress conditions affecting pilots and learners. Dehydration is a critical loss of body water, often from heat, exertion, low humidity at altitude, or insufficient fluid intake, which degrades alertness, judgment, and coordination. Heatstroke is a more severe condition in which the body can no longer regulate its own , usually following prolonged dehydration and heat , resulting in dangerously temperature and potential collapse.