  In the quest of completely describing entanglement in the general case of a
finite number of parties sharing a physical system of finite dimensional
Hilbert space a new entanglement magnitude is introduced for its pure and mixed
states: robustness. It corresponds to the minimal amount of mixing with locally
prepared states which washes out all entanglement. It quantifies in a sense the
endurence of entanglement against noise and jamming. Its properties are studied
comprehensively. Analytical expressions for the robustness are given for pure
states of binary systems, and analytical bounds for mixed states of binary
systems. Specific results are obtained mainly for the qubit-qubit system. As
byproducts local pseudomixtures are generalized, a lower bound for the relative
volume of separable states is deduced and arguments for considering convexity a
necessary condition of any entanglement magnitude are put forward.
