What is duct bank? in which case we use it?

Duct banks are groups of conduits designed to protect and consolidate cabling to and from buildings. In a duct bank, data and electrical cables are laid out within PVC conduits that are bundled together; these groupings of conduit are protected by concrete and metal casings. Duct banks are often buried, allowing contractors to consolidate the wiring for a building into centralized underground paths.