  The existence of non-local quantum correlations is certainly the most
important specific property of the quantum world. However, it is a challenging
task to distinguish correlations of classical origin from genuine quantum
correlations, especially when the system involves more than two parties, for
which different partitions must be simultaneously considered. In the case of
mixed states, intermediate levels of correlations must be introduced, coined by
the name inseparability. In this work, we revisit in more detail such a concept
in the context of continuous-variable quantum optics. We consider a six-partite
quantum state that we have effectively generated by the parametric
downconversion of a femtosecond frequency comb, the full 12 x 12 covariance
matrix of which has been experimentally determined. We show that, though this
state does not exhibit "genuine entanglement", it is undoubtedly
multipartite-entangled. The consideration of not only the entanglement of
individual mode-decompositions but also of combinations of those solves the
puzzle and exemplifies the importance of studying different categories of
multipartite entanglement.
