What happens when quantum symmetry breaks only halfway?

In closed quantum systems, symmetry either holds or breaks — but mixed states in open systems allow a subtler middle ground called strong-to-weak spontaneous symmetry breaking. This review maps how that single idea connects seemingly unrelated phenomena: topological order, emergent hydrodynamics, and information-theoretic measures of quantum phases. It's a conceptual unification story, showing that a familiar statistical-mechanics equivalence (canonical vs. grand-canonical ensembles) quietly underlies a much broader landscape.