Question submitted by Frank Cosco
Oh, this is such a common question. I've taken my answer straight from the Enviroment Canada web site:
The probability of precipitation (POP) is the chance that measurable precipitation (0.2 mm of rain or 0.2 cm of snow) will fall on any point of the forecast region during the forecast period. For example, a 30% probability of precipitation means that the chance of you getting rained over (or snowed over in winter) is 3 in 10. In other words, there is a 30% chance that rain or snow will fall on you, and, therefore, a 70% chance that it won't. It must also be noted that a low POP does not mean a sunny day: it only means a day where the chance of rain or snow is low.