  We introduce a multi-mode squeezing coefficient to characterize entanglement
in $N$-partite continuous-variable systems. The coefficient relates to the
squeezing of collective observables in the $2N$-dimensional phase space and can
be readily extracted from the covariance matrix. Simple extensions further
permit to reveal entanglement within specific partitions of a multipartite
system. Applications with nonlinear observables allow for the detection of
non-Gaussian entanglement.
