身子 (shēn zi) is a colloquial noun for 'body' or 'health', used in everyday speech. It is less formal than 身体 (shēn tǐ, HSK2), which is the standard all-purpose word, and more casual than 人体 (rén tǐ, HSK5), which refers to the human body in a scientific or anatomical sense. 身子 can also euphemistically mean 'pregnancy' (e.g., 有了身子 'to be pregnant'), a sense that 身体 and 人体 do not share.