When a unit volume of a liquid substance is mixed with an appropriate volume of a liquid solvent to obtain a desired concentration, it is called a simple dilution. A series dilution refers to repeating the process of a simple dilution as a more expedient means of obtaining the desired concentration factor. The source of the solute in each step of the series comes from the previous step.
To dilute a solution, more of the solvent is added, or the amount of solute is reduced. In order to obtain a true dilution, one must thoroughly mix the diluted material. The opposite of dilution is to concentrate a solution by either adding more of the solute or reducing the amount of the solvent.