Ethernet to fiber is the process of translating, transferring and communication network data or signals over an Ethernet connection to a fiber-optic based network or network medium.
It is a networking / internetworking technology that enables the connectivity of an Ethernet-based network with a fiber-optic network.
Techopedia explains Ethernet to Fiber
Ethernet to fiber is primarily used when interconnecting a local and slow speed Ethernet based network with a faster Fiber Optic network.
Typically, the interconnection between both the networks is established through purpose built converters. Such converters translate and convert the Ethernet signals / frames / packets into the signals or data supported by the fiber optic network / device.
Usually Ethernet to fiber is implemented at service provider or a data center facility that transmits local data over fiber connection to remote users.