In the weather forecast, the precipitation in an area is 800 mm, what does it actually mean?

Usually refers to the sum of the annual precipitation in this area (precipitation is not equal to rainfall, but also includes snowfall and hail, etc. ). Precipitation is measured by special instruments, and the annual precipitation can reflect the richness of water resources in a region, which is generally expressed in millimeters (international regulations).

Millimeter is a very small unit, and the annual precipitation in some parts of Africa is only a few millimeters, and it doesn't rain almost all year round.

Usually there is a column chart of monthly precipitation in geography books, which reflects the monthly precipitation, such as June, July and August in China. The sum of each month is the precipitation of that year.