星级 (xīng jí) refers to a star rating system (e.g., hotel stars) and can be used as a noun ('star rating') or adjective ('star-rated, top-class'). It implies a formal classification scale, unlike 顶级 (dǐng jí), which means 'top-notch, first-rate' in a general sense without a rating system. Use 星级 when a specific star level is involved (e.g., 五星级酒店).