应用 (yìng yòng) means 'to apply' — using a theory, method, or technology in a practical context, often in formal or technical settings. It is more specific than 使用 (shǐ yòng 'to use, employ'), which is a general-purpose word for using tools or objects. As an adjective, it means 'applied' (e.g., 应用语言学 'applied linguistics'), contrasting with 实用 (shí yòng 'practical, functional'), which describes something that is useful in everyday life.