Glossary
What is a METAR?
A coded observation of the weather at an airport at one moment in time, giving wind, visibility, cloud, temperature, dew point and altimeter setting. It records what is happening, not what is expected.
Also called Aviation routine weather report
That is the whole entry for now. The longer version, with the mechanics and worked examples, is still to be written. See autorotation for how those read once they exist.