"Wǎn ān" is a polite and warm interjection used to bid someone good night, typically before going to sleep. The character 晚 (wǎn) means 'evening' or 'late', and 安 (ān) means 'peace', 'safety', or 'to rest'. Together, they literally convey the wish for a peaceful, restful evening — essentially 'may you have a peaceful night'. It is not a noun describing an object or concept, but rather a fixed phrase used exclusively as a farewell greeting at bedtime.

This expression is appropriate in both formal and informal contexts — spoken to family members, friends, colleagues, or even in written messages like texts or emails before sleeping. Unlike English 'good night', it is rarely used ironically or as part of a longer sentence; it stands alone as a complete, courteous closing. It carries gentle warmth and care, especially when said to children or elders, and reflects Chinese cultural emphasis on harmony and well-wishing in daily interactions.