“First, seen as a formal entity or product, an adaptation is an announced and extensive transposition of a particular work or works. This “transcoding” can involve a shift of medium (a poem to a film) or genre (an epic to a novel), or a change of frame and therefore context: telling the same story from a different point of view, for instance, can create a manifestly different interpretation. Transposition can also mean a shift in ontology from the real to the fictional, from a historical account or biography to a fictionalized narrative or drama. [...]
Second, as a process of creation, the act of adaptation always involves both (re-)interpretation and then (re-)creation; this has been called both appropriation and salvaging, depending on your perspective. [...]
Third, seen from the perspective of its process of reception, adaptation is a form of intertextuality: we experience adaptations (as adaptations) as palimpsests through our memory of other works that resonate through repetition with variation.”