A supersaturated solution is a solution that contains more solute than what the solvent can dissolve.
In a normal solution, the solvent is greater than the solute for it to dissolve, hence a supersaturated solution is different.
The most common example is the supersaturated Sodium Acetate. A supersaturated solution of sodium acetate looks very cool when you drop a sodium acetate crystal into its supersaturated solution and the excess sodium acetate grows out crystals.