One fiber and single fiber and WDM and BiDi

WDM is an abbreviation for Wavelength Division Multiplex. BiDi is called bi-direction as well.

All of them (one fiber/ single fiber/ WDM/ BiDi) mean to transmit and receive data with two different wavelengths such as TX 1310nm and RX 1550nm through one fiber. For example, BiDi sfp transceivers also refer to single fiber SFP transceivers and one fiber SFP transceivers. Single fiber bi-directional optical transceiver components are with one connector. Either LC or SC connectors are available for transmitting and receiving. Single fiber bidirectional transceivers, fiber media converters and devices are widely used in telecommunication applications, in order to achieve lower cost. The price of WDM transceivers is little more expensive however they dramatically save the cost of long distance fiber.