  We observe that a term of the WZW-type can be added to the Lagrangian of the
Poisson Sigma model in such a way that the algebra of the first class
constraints remains closed. This leads to a natural generalization of the
concept of Poisson geometry. The resulting "WZW-Poisson" manifold M is
characterized by a bivector Pi and by a closed three-form H such that
[Pi,Pi]_Schouten = < H, Pi^3 >.
