  Among all entanglement measures negativity arguably is the best known and
most popular tool to quantify bipartite quantum correlations. It is easily
computed for arbitrary states of a composite system and can therefore be
applied to discuss entanglement in an ample variety of situations. However, its
direct physical meaning has not been pointed out yet. We show that the
negativity can be viewed as an estimator of how many degrees of freedom of two
subsystems are entangled. As it is possible to give lower bounds for the
negativity even in a device-independent setting, it is the appropriate quantity
to certify quantumness of both parties in a bipartite system and to determine
the minimum number of dimensions that contribute to the quantum correlations.
