想正确的理解最好是结合上下文

marginal shareholder就是潜在的最有可能的持股者（就是即将要买入股票的人）
因为在汉语里面要描述这种经济社会的状态比较难，因为抽象。我列举一段话，你看下就明白了
However, in the past, some shareholders were, like the animals in Orwell's Animal Farm, more equal than others. (And even today, large shareholders still are.) But Reg FD eliminated a lot of the discrimination against small shareholders by making information publicly available to all shareholders at the same time. That, along with the growth of the internet and easy dissemination of information and the growth of individual stock ownership, has led to the marginal shareholder (you and me, unless you are running a mutual fund or something) having the same access to things like quarterly earnings conference calls and other things once reserved strictly for Wall Street.