Sentence:  We have already alluded to <WSD>decoherence</WSD> in connection with the emergence of classical space-time, the ‘collapse′ of the wave function (Case 3) and the notion of entanglement. Physicists have hailed the discovery of <WSD>decoherence</WSD> as ‘the most important advance in the foundation of quantum theory since Bell's inequalities.'131 This praise is based on good reasons: (a) <WSD>decoherence</WSD> offers new ways of understanding quantum mechanics for it embodies a critique of entrenched terminology (‘collapse' of the wave function, complementarity); (b) it is testable since it appeals to physical processes; (c) it offers an insight into a much more fundamental level of quantum indeterminacy. 
Meaning of the word marked with <WSD> tags:  Loss of quantum coherence (phase relation between the quantum states of particles) in a physical system as it interacts with its environment.