买东西。

The phrase '买东西' (mǎi dōng xi) literally translates to 'buy east west.' Its origin dates back to ancient China, specifically to the Tang Dynasty (618-907 AD). During this period, the capital city of Chang'an (modern-day Xi'an) had two major markets: the East Market (东市, dōng shì) and the West Market (西市, xī shì). These markets were prominent commercial centers where people would go to buy all sorts of goods. Over time, the act of going to these markets to purchase items became synonymous with shopping in general. Thus, '买东西' evolved from literally referring to buying goods from the East and West markets to broadly meaning 'to purchase goods' or 'to go shopping,' regardless of the specific location. It became a common idiom that has persisted in the Chinese language for over a thousand years, illustrating a fascinating connection between linguistic development and historical commercial practices.