We define the Maslov index of a
loop tangent to the characteristic foliation of a coisotropic submanifold as the mean
Conley–Zehnder index of a path in the group of linear symplectic transformations,
incorporating the “rotation” of the tangent space of the leaf — this is the standard
Lagrangian counterpart — and the holonomy of the characteristic foliation. We also
show that, with this definition, the Maslov class rigidity extends to the class of the
so-called stable coisotropic submanifolds including Lagrangian tori and stable
hypersurfaces.