  We present an operational interpretation of quantum discord based on the
quantum state merging protocol. Quantum discord is the markup in the cost of
quantum communication in the process of quantum state merging, if one discards
relevant prior information. Our interpretation has an intuitive explanation
based on the strong subadditivity of von Neumann entropy. We use our result to
provide operational interpretations of other quantities like the local purity
and quantum deficit. Finally, we discuss in brief some instances where our
interpretation is valid in the single copy scenario.
