虚幻 (xū huàn) describes something that is illusory, dreamlike, or not real — it points to the quality of being an illusion (like a mirage or a fantasy). Unlike 虚假 (xū jiǎ), which means 'false, phony' (often for claims or products), and 虚 (xū) meaning 'empty/unreal' in a broader sense, 虚幻 is more abstract and poetic, emphasizing the lack of substance in perception or imagination.