middle class

Social Class usually comprising of white-collar (non-manual) workers, lower-level managers, and small business owners, often constituting about one-third of the employed population of a country. 

The income of this class is higher than that of the working-class but lower than that of the upper-middle class (doctors, engineers, lawyers, middle-size business owners) and upper class. 

comprise
〔全体が部分として〕～を包む［包含する］
〔部分〕から成る

comprise a steering committee
運営委員会を構成する