The amount of substance in given unit volume is called concentration. Concentration is a measure of the amount of solute dissolved in a given amount of solvent or solution. It is expressed in various units, such as moles per liter (M), grams per liter (g/L), parts per million (ppm), or percent by volume (%v/v), among others. Concentration plays a crucial role in understanding the behavior of solutions, reaction kinetics, and various chemical processes.