What Is Flight Level? Definition & Meaning in Aviation
A flight level (FL) is an altitude expressed in hundreds of feet above the standard pressure level of 1013.25 hPa, for example FL350 is about 35,000 feet.
In plain language
Above a set altitude all aircraft use the same standard pressure reference, so that they all measure height the same way and keep their separation.
Example
An aircraft cruising at FL370 over Pakistan is at about 37,000 feet, or about 11,300 metres.
Why it matters
Flight levels are the common language of cruising altitudes. If you see FL350 on a chart or a feed, it means about 35,000 feet, measured on the standard pressure setting.