To begin, let’s discuss what the parts of a solution are. A solution consists of two things: a solvent and a solute. In most solutions you will encounter, the solvent will likely be water, which can dissolve so many things that we call it the “universal solvent!” A solute can be practically anything that can dissolve in water: sugar, salt, soap, a chemical, hot cocoa mix, etc. Note that other things besides water can be solvents as well. For example, if you heat milk on the stove and add sugar and cocoa powder to make hot chocolate, the milk is the solvent and the sugar and cocoa are the solutes.
A solution is formed when a solvent and a solute are mixed together. A saturated solution is formed when some solute is added to the solvent, but not all of the solute can be dissolved by the solvent, leaving some remaining at the bottom of the container or just hanging out in the solution, no matter how much the solution is mixed.
Now for a whole new spin on things: when you heat a saturated solution, the solvent is able to hold even more of the solute, and some or all of the solute that was just hanging out in the solution disappears as it dissolves into the solvent, forming a supersaturated solution! A supersaturated solution can only keep that larger amount of solute dissolved in the solution while it remains at a certain higher temperature, so as the solution cools, it becomes unstable and some of the solute will begin to crystallize back out of the solution as the temperature of the solution lowers. This means that a supersaturated solution is a great place to start when you are trying to grow crystals, just as we did in the rock candy science experiment!