The correct term to fill in the blank is "supersaturated solution."
So, the complete sentence would be:
"A solution which contains more amount of solute than that is required to saturate it, is known as a supersaturated solution."
In a supersaturated solution, the solution has been prepared by dissolving more solute than it can normally hold at a given temperature. This is typically done by heating the solvent, dissolving the solute, and then slowly cooling the solution. These solutions are unstable and can rapidly crystallize if disturbed.