楼主好，推荐一本书：《微观经济学》（易纲  海闻  主编   周惠中 著  上海人民出版社  2003版）第245页。
  边际购买者（marginal buyer）又称边际消费者，指在给定企业供给地点的条件下，在任何一家企业购买产品时，所得效用无差异的消费者。
  边际消费者这一概念最初出现于霍特林的地点模型中。该模型的主要特点是用不同地点代表消费者的不同偏好。所以边际消费者这一概念可用于结合消费者效用类型分析市场均衡问题。
  
  如果楼主觉得在下的回答对您有帮助，请不吝评分吧。

2# shunzqc

你的解释挺好的~我们学的是曼昆的那本经济英文版...

但是他对边际的概念解释基本米有，你能帮我解决下边际这个问题吗?

多谢了!

The marginal buyer is the one whose maximum buying price is just two and a half; a slightly higher selling price would drive him out of the market. Under the law of price uniformity, all the exchanges are made at the equilibrium price (once it is estab­lished), i.e., between the valuations of the marginal buyer and those of the marginal seller, with the demand and supply sched­ules and their intersection determining the point of the margin. It is clear from the nature of human action that all buyers will benefit (or decide they will benefit) from the exchange. Those who abstain from buying the good have decided that they would lose from the exchange. These propositions hold true for all goods.

我觉得就是在equilibrium的状态下，价格只要稍微上涨，marginal buyer们就不会再购买；同理价格只要稍微下调，marginal seller就不会出售。不晓得理解对不对