'似曾相识' literally means 'seemingly have met before' — each character contributes: 似 (seems like), 曾 (already, once), 相 (mutually, each other), and 识 (to know, to recognize). Together, they express the uncanny feeling that a current experience — a place, face, phrase, or sensation — is strangely familiar despite no conscious memory of encountering it before. It captures the psychological phenomenon of déjà vu, often evoking wonder, nostalgia, or mild disorientation.

This phrase is commonly used in literary, reflective, or introspective contexts — in novels, essays, poetry, or thoughtful conversation — rather than casual speech. It carries a poetic, slightly melancholic or philosophical tone. While grammatically flexible (functioning as a noun or adjective), it typically modifies nouns ('似曾相识的感觉') or serves as a predicate ('这场景似曾相识'). It’s rarely used in technical or bureaucratic language, and almost never in commands or directives.