A back office is a part of most corporations where tasks dedicated to running the company itself take place. The term «Back office» comes from the building layout of early companies where the front office would contain the sales and other customer-facing staff and the back office would be those manufacturing or developing the products or involved in administration but without being seen by customers. Although the operations of a back office are seldom prominent, they are a major contributor to a business.
Examples of back-office tasks include IT departments that keep the phones and computers running (operations architecture), accounting, and human resources.
(source: http://en.wikipedia.org/wiki/Back_office)