The word "what" in Japanese is commonly expressed as 何 (nani) or なん (nan), depending on the context and sentence structure. 何 (nani) is the most versatile and standard form, used in questions like 何ですか？ (Nani desu ka?), meaning "What is it?" or "What is this?" In certain grammatical constructions, なん (nan) is used instead, such as in 何時ですか？ (Nanji desu ka?), meaning "What time is it?" The choice between nani and nan often depends on what follows in the sentence. For informal speech, simply saying なに？ (Nani?) can mean "What?" and is commonly used among friends. To add surprise or disbelief, you might hear え？何？ (E? Nani?), translating to "Huh? What?" Japanese communication can vary significantly in tone, so these expressions adapt to both formal and casual conversations.