Plain English Meaning
A short code in a weather report meaning 'flight level follows.' It tells the reader that the next number is a cloud height given in hundreds of feet above sea level using a standard pressure setting, not the usual height above the airport.
Full Definition
In an aviation routine weather report (METAR), /FL is a contraction used in remarks to introduce the height of a cloud layer reported in flight levels (hundreds of feet above mean sea level on the standard altimeter setting of 29.92 inches of mercury) rather than in feet above the ground.
Context Anchor
Seen in coded , especially when checking the of reported , , or along a .