What does 70% rainfall mean?

It means that the probability of rain is 70%.

The general situation of precipitation probability forecast is sunny, and the probability of 0% is impossible to precipitation; Sunny to cloudy, the probability of precipitation between 10% and 20% is very small; Cloudy, sporadic or local precipitation, when the probability is between 30% and 50%, there is a chance of precipitation; Precipitation, the probability is between 60% and 70%, and the possibility of precipitation is relatively large; When it is greater than or equal to 80%, the possibility of precipitation is high; If the probability is 100%, there will definitely be precipitation, and the probability of precipitation in this city is 70%. This is a probability problem, which belongs to a mathematical concept. The intuitive meaning refers to the possibility of a thing happening.