时尚 (shí shàng) is the general word for 'fashion' as a concept (noun) and can also describe something as fashionable (adjective). 时髦 (shí máo) is only an adjective and more colloquial for 'trendy'; 时装 (shí zhuāng) refers specifically to the fashion industry or fashionable clothing. 新潮 (xīn cháo) emphasizes 'new wave/trend' and is often used for styles that are cutting-edge.