middle class

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The socioeconomic class between the working class and the upper class, usually including professionals, highly skilled laborers, and lower and middle management.

from The Century Dictionary.

• Of, pertaining to, or included in the middle class. See middle class, under middle, a.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A social and economic class lying above the working class and below the upper class.
• noun plural The groups in society composed of professionals, semi-professionals, and lower-to-middle managerial level workers.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the social class between the lower and upper classes
• adjective occupying a socioeconomic position intermediate between those of the lower classes and the wealthy