These maps show the chance of precipitation for the next few days. Precipitation includes rain, snow, etc. This is also known as "P.O.P." which means Probability of Precipitation. It does not predict when, where or how much precipitation will occur.
For example: "P.O.P. 60%" This expression means there is a 60% chance that any random place in the forecast area, such as your home, will receive measurable rainfall. Measurable rainfall means at least 0.2 mm of rain or the water equivalent of snow.