'乱说' literally combines '乱' (luàn), meaning 'chaotic', 'disorderly', or 'reckless', and '说' (shuō), meaning 'to speak' or 'to say'. Together, they form a verb meaning 'to talk nonsense', 'to speak without thinking', or 'to make unfounded statements'. It carries a negative connotation and implies carelessness, lack of truthfulness, or inappropriate timing — not just speaking loudly or quickly, but speaking in a way that is irresponsible, inaccurate, or socially inappropriate.

This word is commonly used in everyday spoken Chinese to scold or warn someone — especially children, students, or colleagues — who are spreading rumors, exaggerating, guessing wildly, or making baseless claims. It’s often paired with modal verbs like '别' (don’t) or '不能' (must not), and frequently appears in imperative or admonishing contexts. While it can be used lightly among friends, it’s generally informal and slightly critical, rarely appearing in formal writing or official speech.