Infrastructure typically refers to the technical structures that support a society, such as roads, water supply, wastewater, power grids, floodmanagement systems, communications (internet, phone lines, broadcasting), and so forth. In the past, these systems have typically been owned and managed by local or central governments. These various elements may collectively be termed civil infrastructure, municipal infrastructure, or simply public works, although they may be developed and operated as private-sector or government enterprises. A more generic definition of infrastructure is the network of assets "where the system as a whole is intended to be maintained indefinitely at a specified standard of service by the continuing replacement and refurbishment of its components."

In other applications, infrastructure may refer to information technology, informal and formal channels of communication, software development tools, political and social networks, or beliefs held by members of particular groups. Still underlying these more general uses is the concept that infrastructure provides organizing structure and support for the system or organization it serves, whether it is a city, a nation, or a corporation. Economically, infrastructure could be seen to be the structural elements of an economy which allow for production of goods and services without themselves being part of the production process, e.g. roads allow the transport of raw materials and finished products.

Typical attributes

Infrastructure assets generally have the following attributes:

• They are large networks constructed over generations which are not often replaced as a whole system
  
• The system or network has a long and indefinite life because its service capacity is maintained in perpetuity (by continual refurbishment or replacement of components as they wear out).
  
• The system components are interdependent and not usually capable of subdivision or separate disposal, and consequently are not readily disposable within the commercial marketplace.
  
• The system interdependency may limit a component life to a lesser period than the expected life of the component itself.
  
• The assets have a high initial cost and a value which is difficult to determine.

An asset can be considered to be part of the infrastructure when it is an integral part of a total system, i.e. if the asset is removed the system is incomplete, or the particular asset is necessary for the system to deliver the required standard of service.

Critical infrastructure

The term "critical infrastructure" has been widely adopted to distinguish those infrastructure elements that, if significantly damaged or destroyed, would cause serious disruption of the dependent system or organization. Storm, flood, or earthquake damage leading to loss of certain transportation routes in a city (for example, bridges crossing a river), could make it impossible for people to evacuate and for emergency services to operate; these routes would be deemed critical infrastructure. Similarly, an on-line booking system might be critical infrastructure for an airline.