When solids are mixed in a liquid solvent, three types of solutions are possible depending on how much solute is added. Recall that the solubility of a solute is defined as the maximum amount that can be dissolved in a solvent. Solubility of most compounds increases with increasing temperature. An unsaturated solution results when there is less than the maximum amount of solute dissolved. This type of solution will appear homogenous. A saturated solution results when there is more solute than is soluble in the solution. This solution will be heterogenous; solid in excess of the solubility will remain undissolved on the bottom of the container. A super saturated solution must be prepared from a saturated solution by heating it so that all of the solute dissolves and then cooling carefully so that no precipitate forms.
Check out the video below for more details and how to read solubility curves.
Solubility of MgCl