When dealing with many-body systems made of identical particles, the usual definition of separability (absence of quantum correlations) appears problematic since the natural particle tensor product structure on which it is based is no longer available. A generalized notion of quantum correlation (entanglement) not explicitly referring to the set of system states is needed and it can be given in terms of the algebra of observables and of the behaviour of the associated correlation functions. This change of paradigm has direct applications in quantum technology: it allows constructing quantum sensors able to outperform any known, classical apparatus.