Sterling defines a derivative work as:
"... works which are based on other works."
The Berne Convention on Copyright, at 2(3) defines derivative works as follows:
"Translations, adaptations, arrangements of music and other alterations of a literary or artistic work shall be protected as original works without prejudice to the copyright in the original work."
Similarly, Title 17 of the US Code,on Copyrights, defines derivative works as follows:
"A derivative work is a work based upon one or more preexisting works, such as a translation, musical arrangement, dramatization, fictionalization, motion picture version, sound recording, art reproduction, abridgment, condensation, or any other form in which a work may be recast, transformed, or adapted. A work consisting of editorial revisions, annotations, elaborations, or other modifications, which, as a whole, represent an original work of authorship, is a derivative work."
Derivative works walk a fine line between copyright infrigement and eligibility for copyright protection. Generally, the test will be whether there is sufficient originality in the alleged derivative work; that it constitutes an original work in its own right.
Some jurisdictions do not use the term derivative work but nonetheless extend copyright protection to such original works through the relevant copyright statute. For example, Canada's Copyright Act awkwardly includes derivative works within the definition of "every original literary, dramatic, musical and artistic work" as follows (emphasis added):
"Every original literary, dramatic, musical and artistic work includes every original production in the literary, scientific or artistic domain, whatever may be the mode or form of its expression, such as compilations, books, pamphlets and other writings, lectures, dramatic or dramatico-musical works, musical works, translations, illustrations, sketches ...."