turnover  noun
①Countable and uncountable(money taken)[一定时期内的] 营业额
  a high/low turnover          高/低营业额
  a turnover of £20,000       20,000英镑的成交量
②Countable and uncountable(replacement rate)(of staff)人员调整率 (of stock)货物周转率 
Turnover is an accounting term that calculates how quickly a business collects cash from accounts receivable or how fast the company sells its inventory. In the investment industry, turnover represents the percentage of a portfolio that is sold in a particular month or year. A quick turnover rate generates more commissions for trades placed by a broker.
其实你只要记得是 一定时间段内的量 
然后再联系上下文就很好理解了