Concept: Copyright protects original works from unauthorized use. Infringement occurs when someone uses, copies, distributes or adapts a work without permission.
Step 1: Check Assertion A.
Copyright infringement means unauthorized use of copyrighted work without permission of the copyright holder.
\[
A = \text{Correct}
\]
Step 2: Check Reason R.
A derivative work is based on an existing work. For example, a film based on a novel is a derivative work.
\[
R = \text{Correct}
\]
Step 3: Check explanation.
Reason R explains derivative work, but it does not directly explain the definition of copyright infringement.
Therefore, both A and R are correct, but R is not the correct explanation of A.