In quantum physics, some of the most interesting effects are the result of interferences. Decoherence, or loss of coherence, occurs when a quantum system eventually loses the ability to produce interferences, due to external noise or coupling to a larger and unmonitored system (i.e. the surrounding environment).
Source:
https://phys.org/news/2019-11-anomalous-coherence-dissipative-many-body.html