noun
first-class; top-notch; leading
Describes something of the highest rank or quality, often used for people, institutions, or works.
彼は第一流のピアニストだ。
He is a first-class pianist.
このホテルは第一流のサービスを提供している。
This hotel provides top-notch service.
Means 'the best' or 'supreme', often used in casual praise. 第一流 is more about established rank or class.
Compound of 第一 (first, number one) and 流 (style, school, class). The combination straightforwardly means 'first-class' or 'top rank'.