关于profit margin

Profit margin = Net profit margin
Gross profit margin毛利率

Profit margin, net margin, net profit margin or net profit ratio all refer to a measure of profitability. It is calculated by finding the net profit as a percentage of the revenue.
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margin是差额，但是这个词组就是利润率的意思。
解释是说，profit margin=net margin=net profit，都是用来计算获利能力的。净利率是指（扣除tax之后的net income/sales)
这些用词是固定短语，如果你要非按字面翻译，那我就没办法解释了。

margin的本意是“余地、范围”，所以profit margin就是利润空间，说利润率是引申了的。毛利就有点远了。

profit margin
n. 利润率
例句:
In this instance, the only known is our actual profit margin.
在这种场合下，唯一能知道的事是我们实际可得的利润
The computer has been programmed (to calculate the gross profit margin on all sales).
计算机已输入了程序指令(以计算各项销售的毛利率).
My business has been through a bad patch recently and I have been unable to maintain a reasonable profit margin.
最近我的买卖经历了一段不景气的时光，我已不能保持适当的利润率。