Final answer:
Conservation refers to the cognitive ability in children to understand that changes in appearance do not alter an object's basic properties. It develops during Piaget's concrete operational stage and reflects the understanding of reversibility and the departure from egocentrism.
Step-by-step explanation:
The awareness of young children that helps them to know that altering an object's or a substance's appearance does not change its basic properties is referred to as conservation. According to Jean Piaget, conservation is a cognitive ability that develops in children around the age of 7 to 11 years old, which he termed the concrete operational stage. During this stage, children learn that despite changes in the form of a substance or object, the amount, volume, or number remains the same as long as nothing is added or removed. This shows the child's understanding of the principle of reversibility, which Piaget described as the ability to revert an object back to its original form or condition after some change has occurred, such as pouring water from one glass to another and back again without change in volume. This cognitive development milestone indicates a departure from egocentrism and the onset of logical thinking about the physical world.