Exactly what does 50% chance of rain mean?

It means it is going to rain, or it isn’t going to rain.  Don’t we already know that?  This is the biggest scam employment opportunity ever conceived.  After spending years of training in schools across the country, degrees in meteorology, masters programs in post doctoral work, the best estimate they can come up with for the weekend weather is a `50% chance of rain`. 

This is an occupation that seriously needs governmental intervention.   Freakin’ scam, I tell you!