Which term refers to a solution that contains less solute than the solvent can normally hold?

The term that refers to a solution containing less solute than the solvent can normally hold is "unsaturated." An unsaturated solution is one in which the concentration of solute is lower than the maximum solubility limit at a given temperature and pressure. This means that if more solute is added to the solution, it will continue to dissolve until the saturation point is reached.

In contrast, a saturated solution occurs when the maximum amount of solute has been dissolved in the solvent, and any additional solute will not dissolve. A supersaturated solution is one that has been altered to temporarily hold more solute than it normally can at equilibrium, often achieved by changing the temperature or pressure. Lastly, a concentrated solution contains a high amount of solute relative to the volume of solvent, but this term does not necessarily relate to the solubility limit. Therefore, the correct term for a solution containing less solute than the solvent can normally hold is indeed "unsaturated."