From Mises Wiki, the global repository of classical-liberal thought
A convertible good is one that can be adapted to serve more than one purpose. For example, a station wagon with a seat that folds down to allow for cargo to be transported rather than passengers is a convertible good. So is, for that matter, a convertible; it can be adapted to fulfil the function of either letting in sunlight and fresh air or providing shelter from the elements. The opposite of a convertible good is an inconvertible good. In some respects, a printed book would be relatively inconvertible compared to a computer tablet, because it can only display the text of one book.