脑袋 (nǎo dai) is the colloquial, everyday word for 'head', often used in speech for the physical head or figuratively for the mind ('use your head'). It is more informal than 头 (tóu), which is the standard neutral word for 'head', used in compounds and formal contexts. Compared to 脑子 (nǎo zi), which emphasizes the brain as an organ or intelligence, 脑袋 often refers to the whole head or one's thinking ability in a casual way.