profit margin       
noun [ C ] uk/ˈprɒf.ɪt ˌmɑː.dʒɪn/ us/ˈprɑː.fɪt ˌmɑːr.dʒɪn/
 利润率,利润幅度
the difference between the total cost of making and selling something and the price it is sold for
  Many small companies operate on very narrow profit margins. 许多小公司靠非常微薄的利润率维持经营。