For a shared quantum entanglement resource, one party's choice of measurement can prepare different conditional ensembles for the distant party. Discarding the outcome leaves the same distant reduced density matrix, so steering does not itself permit signalling. Demonstrating steering against a local hidden-state model is stronger than merely observing a change in a postselected description.
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Quantum steering is a phenomenon in quantum mechanics that involves the ability of one party (often referred to as Alice) to affect the state of another party's (Bob's) quantum system through local measurements, even when the two parties are separated by a distance. This concept is closely related to other foundational aspects of quantum mechanics, such as entanglement and Bell's theorem.