Final answer:
The ability to refer to objects using language when they are not present is known as symbolic representation. It differs from object permanence, which is knowing that objects still exist even when not perceived.
Step-by-step explanation:
Having the ability to refer to an object using language, even when the object is not present, is known as symbolic representation. This concept allows individuals to communicate and think about things that are not immediately visible or tangible, using language as a tool to represent those objects in the mind. In contrast, object permanence is the understanding that objects continue to exist even when they cannot be seen, heard, or touched, which is a developmental milestone achieved in early childhood. Thus, option a is correct.