Conservation refers to the concept that physical changes do not alter the mass, weight, number, or volume of matter. This concept is acquired during the concrete operational stage of cognitive development. Conservation is Piagetian term for the realization that certain quantitative attributes of objects remain unchanged unless something is added to or taken away from them.

Such characteristics of objects as mass, number, area, and volume are capable of being conserved. Moreover, Conservation refers to the recognition that the properties of an object or substance do not change when its appearance is altered in some superficial way. In cognitive psychology, it is the principle that properties of substances such as weight and mass remain the same (are conserved) when superficial characteristics such as their shapes or arrangement are changed.