请教如何理解“margin”或者marginal benefits/costs
我是初学者，只知道这个翻译成“边际。。。”，可是实在不能理解“边际”的意思，只好认为这个翻译很差劲
我查了韦氏词典，认为最好的解释是第4a或者第5个,可是为什么要翻译为让人误导的"边际"呢?望大家释疑.

1 : the part of a page or sheet outside the main body of printed or written matter
2 : the outside limit and adjoining surface of something : edge <at the margin of the woods> <continental margin>
肯定不是前两个吧,可是翻译过来很像是第2个"边缘\边际",让人百思不得其解?
3 a : a spare amount or measure or degree allowed or given for contingencies or special situations <left no margin for error>
这个也不是
b (1) : a bare minimum below which or an extreme limit beyond which something becomes impossible or is no longer desirable <on the margin of good taste> (2) : the limit below which economic activity cannot be continued under normal conditions
不是这个
c : an area, state, or condition excluded from or existing outside the mainstream <the margins of critical discourse — Barbara L. Packer> <living in society's margins>也不是这个
4 a : the difference which exists between net sales and the cost of merchandise sold and from which expenses are usually met or profit derived " 利润",用这个似乎还好理解些 阿?
b : the excess market value of collateral over the face of a loan 这个是什么意思,没看懂
c (1) : cash or collateral that is deposited by a client with a commodity or securities broker to protect the broker from loss on a contract (2) : the client's equity in securities bought with the aid of credit obtained specifically (as from a broker) for that purpose
不懂
d : a range about a specified figure within which a purchase is to be made不是
5 : measure or degree of difference
<the bill passed by a one-vote margin>这个么?