细说 means 'to explain in detail' or 'to elaborate'. The character 细 (xì) literally means 'fine', 'detailed', or 'careful', while 说 (shuō) means 'to speak' or 'to say'. Together, they form a verb expressing the act of speaking carefully and thoroughly — not just briefly stating something, but unpacking it with clarity, examples, or step-by-step reasoning. It often implies intentionality and patience on the part of the speaker.

This word is commonly used in formal, educational, or explanatory contexts — such as lectures, technical instructions, academic writing, or thoughtful conversations where depth matters. It’s slightly more literary or refined than everyday alternatives like 说明 (shuōmíng) or 讲清楚 (jiǎng qīngchu), and is rarely used in casual speech among friends. You’ll often see it after verbs like 请 (qǐng, 'please') or 想 (xiǎng, 'would like to'), signaling a polite or earnest request or offer to elaborate.