"Flight Level" refers to a standardized altitude used in aviation, measured in feet above sea level. It is expressed in hundreds of feet, such as FL250 for 25,000 feet. Flight levels are crucial for maintaining safe vertical separation between aircraft in the sky, especially in controlled airspace. Pilots and air traffic controllers use flight levels to communicate altitude information clearly. When flying at high altitudes, aircraft transition from altitudes measured in feet to flight levels to avoid confusion. This system helps ensure that planes maintain safe distances from one another during flight, contributing to overall air safety.