Saturation describes an equilibrium condition, viz.:
"Solid solute "rightleftharpoons" Dissolved solute"
And thus, in a saturated solution, we might typically see some UNDISSOLVED solute, i.e. a crystalline residue, on the bottom or the sides of the flask.
For a given solvent (usually water), a temperature is specified because a hot solution can normally dissolve more solute than a cold solution.
And now attend, because this definition seems to cause a lot of confusion. If the solution contains a GREATER amount of SOLUTE than would be in equilibrium with UNDISSOLVED solute (i.e. a greater amount of solute than does the saturated solution), the solution is said to be "supersaturated".
How could we make a "supersaturated solution"? Well, one way might be to take a saturated solution (with a mass of undissolved solute), give it a good heat blast to bring ALL of the SOLUTE into solution, and cool the flask carefully, so that the crystals do not precipitate out of solution.
"Supersaturation" is a metastable condition, and sometimes, the solution can be brought back to equilibrium, to "saturation", by scratching the sides of the flask, or introducing a seed crystal, and a mass of solute precipitates; sometimes it does so and generates a lot of heat, which represents the heat required initially to bring the solute to supersaturation. After the mass of crystals deposit, the solution is "NOW SATURATED."
"Unsaturation" describes a solution that contains a "LESSER amount of SOLUTE than would be in equilibrium" "with UNDISSOLVED solute"; such a solution is "unsaturated" with respect to the "solute."
For more of the same, see here, and enclosed links.
Note that a definition of "saturation", such as the "solvent holds all the solute that it can", is "MANIFESTLY INADEQUATE and INCORRECT". If you are unclear as to what I have said, ask again, and someone will help you.
