What is Back Office?

Legal Definition
A back office in most corporations is 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 those involved in administration without being seen by customers. Although the operations of a back office are seldom prominent, they are a major contributor to a business. Broadly speaking, back office includes roles that affect the left side (costs) of business' trading statement.

Back offices may be located somewhere other than company headquarters. Many are in areas and countries with cheaper rent and lower labor costs. Some office parks provide back offices for tenants whose front offices are in more expensive neighborhoods. Back office functions can be outsourced to consultants and contractors, including ones in other countries.
-- Wikipedia