What does the term "dark fiber" refer to in the context of networking?

The term "dark fiber" refers to unused optical fiber that is not currently in service. This fiber is physically present and may have been installed for future use, but it has not been activated or connected to any active transmission equipment. The concept of dark fiber arises from the growing demand for bandwidth and the need for additional network capacity, prompting telecom companies to install more fiber optic cables than are currently needed. It is considered "dark" because it does not transmit any data; there are no signals being sent through it until it is lit up, or activated, for operational use. This unused infrastructure can be leased or purchased by companies in need of additional capacity, allowing them to expand their network without the need for new installations.