METAR (Meteorological Aerodrome Report) is a standard ICAO coded message issued every 30 or 60 minutes from aerodromes. It includes: wind direction and speed (with gusts), visibility, present weather (fog, rain, snow), cloud layers, temperature, dew point, and QNH pressure.
Decoded example
LEMD 291030Z 35008KT 9999 FEW040 18/06 Q1022 means: Madrid-Barajas, 29th at 10:30 UTC, wind from 350° at 8 knots, visibility over 10 km, few clouds at 4,000 ft, temperature 18 °C, dew point 6 °C, pressure 1022 hPa. METARs are the basis for operational aviation decision-making.