针对这三个词，首先需要搞清楚这里的“大盘”是什么意思。

大盘其实是术语“大市值”的缩写。市值的计算方法是将公司已发行股票的数量乘以其每股股价。

“市值”的英文比较常见，market capital，因而大盘股、中盘股、小盘股分别为“big cap stocks”、“mid-cap stocks”以及“small cap stocks”。

公司的股票通常分为大盘股、中盘股或小盘股。

大盘股big cap stocks。

大盘股是指市值超过 100 亿美元的公司。

Big cap stocks refer to the largest publicly-traded companies with market caps of more than $10 billion like General Electric and Walmart. These companies are also called blue-chip stocks—companies with a history of dependable earnings, solid reputations, and strong financials.

中盘股 mid-cap stocks。

中盘股是市值在20亿美元至100亿美元之间的股票，指流通市值比蓝筹股或大盘股要小，但高于小盘股的一类型股票，数量上占据整个股票市场的主体。

Mid-cap (or mid-capitalization) is the term that is used to designate companies with a market cap (capitalization)—or market value—between $2 and $10 billion. As the name implies, a mid-cap company falls in the middle between large-cap (or big-cap) and small-cap companies. Classifications, such as large-cap, mid-cap, and small-cap are approximations of a company's current value; as such, they may change over time.

小盘股small cap stocks。

小盘股是发行在外的流通股份数额较小的上市公司的股票，市值在3亿至20亿美元之间。中国现阶段一般不超3000万股流通股票都可视为小盘股。

A small-cap is a public company whose total market value, or market capitalization, is about $300 million to $2 billion. The precise figures vary.

以下为相关双语示例，供参考：

但是银行表示，大盘股中仍然有不错的机会供胃口不大的投资商选择。

But the bank says, for investors with a weaker stomach, there are still selected opportunities among the large-cap names. 

在近期的市场上扬行情中，中、小盘股一直表现好于大盘股。

In the recent market rally, small- and mid-cap stocks have performed better than large-caps.