  Entangled physical systems are an important resource in quantum information.
Some authors claim that in fact all quantum states are entangled. In this paper
we show that this claim is incorrect and we discuss in operational way
differences existing between separable and entangled states. A sufficient
condition for entanglement is the violation of Bell- CHSH-CH inequalities
and/or steering inequalities. Since there exist experiments outside the domain
of quantum physics violating these inequalities therefore in the operational
approach one cannot say that the entanglement is an exclusive quantum
phenomenon. We also explain that an unambiguous experimental certification of
the entanglement is a difficult task because classical statistical significance
tests may not be trusted if sample homogeneity cannot be tested or is not
tested carefully enough.
