Saturated means that the solute contains as much substance as can possibly dissolve in it. It will be at equilibrium, since the material going to solid and going to solution will equal. Basically it means that no matter how hard you try, you will not dissolve any more solid in your liquid. For example, take sugar and water. You can add sugar and add sugar and add sugar and stir, but at some point no more sugar will dissolve. It stays as a solid at the bottom of the glass. That's a saturated solution.