An optical line termination (OLT), also called an optical line terminal, is a device which serves as the service provider endpoint of a passive optical network. It provides two main functions:

1. to perform conversion between the electrical signals used by the service provider's equipment and the fiber optic signals used by the passive optical network.
2. to coordinate the multiplexing between the conversion devices on the other end of that network (called either optical network terminals or optical network units).

The diagram below depicts an OLT within a fiber-optic network.