The basic facilities, equipment, services and installations required for the effective operation of a business. The minimum requirement to service customers and keep the 'doors open'. Such costs are more likely to be 'fixed' and immovable, rather than vary directly with the business volume.
The basic services and structure required keeping an enterprise 'open for business'. It covers land, buildings, networks, IT structures, desks, carpets, coffee machines and every facility required to be in business. WARNING - it is not easy to change infrastructure costs very quickly.