The concentration of a solution refers to the amount of solute that is dissolved in a specific volume of solvent.

To elaborate, concentration measures the quantity of a particular substance, known as the solute, that is mixed with another substance, referred to as the solvent. It is typically expressed in terms of mass per unit volume, such as grams per liter ($g/L$) or moles per liter ($mol/L$), the latter of which is commonly known as molarity.

When a solute is dissolved in a solvent, a solution is formed. For instance, when sugar is dissolved in water, sugar serves as the solute and water is the solvent, resulting in a sugar solution. The concentration of this solution is determined by the amount of sugar (the solute) that is dissolved in a specified volume of water (the solvent).

In the field of chemistry, understanding the concentration of solutions is essential as it influences the rate of chemical reactions, the pH of the solution, and the behavior of molecules and ions within the solution. For example, a higher concentration of a reactant can increase the reaction rate because there are more particles available to collide with one another.

To calculate the concentration of a solution, you divide the amount of solute by the volume of the solvent. For example, if you dissolve $20$ grams of sugar in $1$ liter of water, the concentration would be $20 \, g/L$.

It is important to note that a solution with a high concentration is often described as “concentrated,” while one with a low concentration is referred to as “dilute.” Understanding these terms and how to calculate concentration is fundamental in the study of chemistry.