A concentrated solution has a greater amount of dissolved solute than a dilute solution.
A solution is a homogeneous mixture that contains one or more solutes dissolved in a solvent. A concentrated solution has more dissolved solute than a dilute solution. Two ways to indicate the concentration of a solution are mass percent and molarity, M.
Mass percent is determined by dividing the mass of the solute by the total mass of the solution, then multiplying times 100. For example, if a 125 g NaCl solution contains 25 g of the solute NaCl, the mass percent =
Molarity is mol/L, and is determined by dividing the moles of a solute by the volume of the solution in liters. If you have a solution containing 0.35 mol of the solute NaCl dissolved in a 1.5 L solution, then
A concentrated solution has a greater amount of dissolved substance per unit volume of solution.
"Concentrated" and "dilute" alone are qualitative terms, and are somewhat subjective in many cases.
For example, with sodium chloride in water, the maximum amount of sodium chloride that can be dissolved in water at ambient temperature is about 350 g per litre.
350 g of sodium chloride is approximately 6 moles, so something like a 5M aqueous solution of sodium chloride is certainly concentrated. However, a 4M solution aqueous solution of sodium chloride is pretty concentrated too, so the term "concentrated" can be quite broad.
It follows that something like a 0.1M solution of sodium chloride in water could be regarded as "dilute", but again this is only a qualitative term.