Wikipedia:
The middle class are any class in the middle of a societal hierarchy. In Weberian socio-economic terms, the middle class is the broad group of people in contemporary society who fall socio-economically between the working class and upper class. In Marxist terms, middle class commonly refers to either the bourgeoisie before or during capitalism, or some emergent new class within capitalism. In common parlance, middle class refers to a set of culturally distinct contemporary Western cultures that emphasize consumerism and property ownership within capitalism.
就是在工作阶层和上层社会之间的一个阶层。在马克思主义理论里是通常指的是无论是在资本主义或资产阶级之前，或在一些新兴资本主义里的新阶级。通常指西方资本主义社会中强调消费主义和拥有财产的文化
The common measures of what constitutes middle class vary significantly between cultures. In urban India, for example, a family is considered middle class if it resides in an owner-occupied property. In the United States, many families where the primary income-earner is employed in a blue collar job consider themselves middle class。In the United Kingdom their equivalents would likely be termed working class, because the level required to be middle class is commonly believed to be set much higher - and may include private schooling for children, ownership of a sizeable family house, luxuries such as family skiing holidays, and the main income-earner either holding a senior role in the professions or themselves being an owner/director of a corporation.
不同文化中衡量中产阶级的标准可以是非常不同的。在印度城市中，自己有房就被认为是中产阶级了。在美国许多家庭主要收入者是蓝领的也认为自己属于中产阶级。而在英国这种阶层的应该被称为工人阶级(working class)，因为通常认为中产阶级所需要的水准被设得高得多 - 可能包括小孩上私立学校，有很大的family house，奢侈假期例如一家人去滑雪，主要的家庭收入者做高级专职，或者拥有/管理企业
Professional-managerial class
……
This group of middle class professionals are distinguished from the rest of the class by training and education (typically business qualifications and university degrees), with example occupations including academics and teachers, social workers, engineers, managers, nurses, and middle-level administrators.
在中国，2005年国家统计局根據人均GDP和购买力平价給出中産階級的家庭年收入在6萬至50萬人民幣之間的結論
根据香港政府统计处的定义，每个月收入1万至4万港元的住户列为中产住户，这类住户占了整体住户数目的55%。
就收入而言，美国的通产家庭年收入在3至20萬美元的即可認爲屬于中産階級，據估計大約80%的美国人屬于中産階級。
个人觉得英国的middle class其实应该是小资产阶级，而不是通常意义上的中产阶级
senior role of professionals —— 那senior engineer算不算呢？这可是一大把的到处都有，我公司的同事大多都是这个级别以上的。可是在伦敦还是买不起大house啊。