saturated solution

I don't understand its meaning....

A saturated solution is a solution with also a precipitate??
Or only a solution without precipitate and with Q = ks ??

For example if I know that I have a saturated solutuion of PbSO4 5*10-4 M , can i say that
[Pb2+] is 5*10^-4 ??
(that is equal to say that in a saturated solution all the salt(s) ,here PbSO4 5*10-4M, is dissociated...


Thanks!!!!!!