Final answer:
Object permanence usually develops between 5 and 8 months old, and it refers to the understanding that even if something is out of sight, it still exists.
Step-by-step explanation:
Object permanence usually occurs between the ages of 5 and 8 months old, according to Piaget's theory of cognitive development. It refers to the understanding that even if something is out of sight, it still exists. For example, if a toy is hidden under a blanket, infants who have developed object permanence will reach for the hidden toy, indicating that they know it still exists.