  A new measure based on the tripartite information diagram is proposed for
identifying quantum discord in tripartite systems. The proposed measure
generalizes the mutual information underlying discord from bipartite to
tripartite systems, and utilizes both one-particle and two-particle projective
measurements to reveal the characteristics of the tripartite quantum discord.
The feasibility of the proposed measure is demonstrated by evaluating the
tripartite quantum discord for systems with states close to
Greenberger-Horne-Zeilinger, W, and biseparable states. In addition, the
connections between tripartite quantum discord and two other quantum
correlations---namely genuine tripartite entanglement and genuine tripartite
Einstein-Podolsky-Rosen steering---are briefly discussed. The present study
considers the case of quantum discord in tripartite systems. However, the
proposed framework can be readily extended to general N-partite systems.
