A concentration gradient refers to the difference in concentration of a particular substance between two regions. There are several synonyms used for this term. Some of the commonly used synonyms include concentration difference, concentration slope, concentration gradient difference, concentration gradient force, and concentration differential. Other words used to refer to concentration gradient include gradient of concentration, concentration flux, concentration step, and concentration change. In some cases, specific terms may be used to refer to the concentration gradient of a particular substance such as pH gradient, ion gradient or electrochemical gradient. Regardless of the terminology used, concentration gradient is an important concept in many fields of science including biology, chemistry, and physics.