<p>Equilibrium = saturated solution?
And then when you add one more bit of solute to a saturated solution, does it become supersaturated and start to crystallize immediately?</p>
<p>Is this right? You know you have a saturated solution when nothing is happening. You know you have a supersaturated solution when there is crystallization. And you know you have an unsaturated solution when...?/</p>
<p>If you add more solute than is saturated, then yes, it should start to crystallize immediately. This also fits in with the concept of its equilibrium shifting to favor the original solid if additional dissolved solute is added. It's possible for a solution to be not reacting and unsaturated. For example, if a solution can handle 5 moles of compound X and dissolve it but only 3 moles of X is present. Technically, more can be dissolved in the solution, but all of it has dissolved so nothing should be happening. I'm not sure how to tell if a solution is unsaturated, but you can figure it out depending on background info (ie, alkenes are unsaturated).</p>