fungibility

In economics and law, fungibility is the property of something whose individual units are considered fundamentally interchangeable with each other.

For example, the fungibility of money means that a $100 bill (note) is considered entirely equivalent to another $100 bill, or to twenty $5 bills and so on, and therefore a person who borrows $100 in the form of a $100 bill can repay the money with another $100 bill, with twenty $5 bills and so on. Non-fungible items are not considered substitutable in the same manner, even if essentially identical.