Derivative Works 2.0: Reconsidering Transformative Use in the Age of Crowdsourced Creation Lipton, J. D., & Tehranian, J. (2015). Derivative Works 2.0: Reconsidering transformative use in the age of crowdsourced creation. Northwestern University Law Review, 109(2), 383–443.
A derivative work is a work that is taken from an already existing source, but you need permission to make a derivative work from the original author. Examples of modifications to original works can be a translation, a book turned into a play, condensed version, etc.