Phys.org has reported:

Quantum phases of matter challenge familiar ways of classifying materials, according to a report on new stability rules that distinguish phases an older method grouped together. Unlike common phases, their properties can overturn traditional ideas about what defines a phase.

Solids keep their shape, liquids flow while maintaining a constant volume, and gases expand to fill their container. Quantum phases are more difficult to categorize, requiring physicists to reconsider their definitions.