An unsaturated solution contains less than the maximum soluble material, while a saturated solution contains all of the material that it is able to dissolve in its current state, with excess material remaining undissolved. A supersaturated solution holds more of the solvent than it would be able to under normal circumstances.
A solution that is unsaturated does not have excess material or solvent within the liquid. Unsaturated solutions have the potential to effectively dissolve more material before reaching the point of full saturation.
A saturated solution is as saturated as it can possibly be under normal conditions. This means that the temperature of the solution, the force applied to it and any other variables are neutral and within normal ranges. A saturated solution is unable to dissolve or absorb any further solvent, and any solvent that is added after this saturation point remains whole, usually floating to the bottom of the solution's container.
Supersaturated solutions are not possible under normal, unmodified circumstances. In order to supersaturate a solution, temperature can be raised, which allows more solvent to be dissolved into the solution. Alternatively, high pressure can create a supersaturated solution. The third way to produce supersaturated solution is to change volume, such as by evaporation.