The probability of precipitation, also referred to as chance of precipitation or chance of rain, can be expressed using descriptive terms instead of numerical values, such as "slight chance."
A probability of precipitation (POP), also referred to as chance of precipitation or chance of rain, is a measure of the probability that at least some minimum quantity of precipitation will occur within a specified forecast period and location. The probability of precipitation can also be expressed using descriptive terms instead of numerical values. For instance, the NWS might describe a precipitation forecast with terms such as "slight chance" meaning 20% certainty and "scattered" meaning 3050% areal coverage. 
