潮流 (cháo liú) is the common noun for 'trend' in fashion, society, or ideas, and also literally means 'tide/current'. 趋势 (qū shì) is a more general 'tendency' used in data, economics, or development; 风尚 (fēng shàng) is a more formal, written term for 'prevailing custom'. The shorter 潮 (cháo) and 新潮 (xīn cháo) are more colloquial and often used as adjectives meaning 'trendy'.