The word 波斯 is formed through a process of phonetic borrowing from a foreign language into Chinese. It is a transliteration, specifically representing the sound of "Persia" (likely entering Chinese via ancient Silk Road contact with the Persian Empire or its intermediaries). The two characters, 波 (bō, meaning "wave") and 斯 (sī, a classical particle or "this"), were chosen not for their individual meanings but because their combined pronunciation in Middle Chinese closely approximated the foreign name, creating a fixed, bisyllabic term for the region and its people.