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The Shop floor literally is the floor

Floor

A floor is the walking surface of a room or vehicle. Floors vary from simple dirt in a cave to many-layered surfaces using modern technology...

 of a factory

Factory

A factory or manufacturing plant is an industrial building where laborers manufacture goods or supervise machines processing one product into another. Most modern factories have large warehouses or warehouse-like facilities that contain heavy equipment used for assembly line production...

 (machine shop) where people work on machines, or the space in a retail

Retail

Retail consists of the sale of physical goods or merchandise from a fixed location, such as a department store, boutique or kiosk, or by mail, in small or individual lots for direct consumption by the purchaser. Retailing may include subordinated services, such as delivery. Purchasers may be...

 establishment where goods are sold to customers. It is opposed to offices and so forth providing accommodation to the business's management

Management

Management in all business and organizational activities is the act of getting people together to accomplish desired goals and objectives using available resources efficiently and effectively...

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In the UK, a worker "on the shop floor" may be used metaphorically sometimes as a synonym

Synonym

Synonyms are different words with almost identical or similar meanings. Words that are synonyms are said to be synonymous, and the state of being a synonym is called synonymy. The word comes from Ancient Greek syn and onoma . The words car and automobile are synonyms...

 for the working class

Working class

Working class is a term used in the social sciences and in ordinary conversation to describe those employed in lower tier jobs , often extending to those in unemployment or otherwise possessing below-average incomes...

 in economic classes C/D/E. In that way it may have undertones of class prejudice, but it may just be meant for an average person, the man on the Clapham Omnibus.