From Wikipedia:
METAR is a format for reporting weather information. A METAR
weather report is predominantly used by pilots in fulfillment of a
part of a pre-flight weather briefing, and by meteorologists, who
use aggregated METAR information to assist in weather forecasting.
Raw METAR is the most popular format in the world for the
transmission of weather data. It is highly standardized through the
International Civil Aviation Organization (ICAO), which allows it
to be understood throughout most of the world.