Hi,
BiDi SFP transceiver is a compact optical transceiver module which uses WDM (wavelength division multiplexing) technology and is compliant with the SFP multi-source agreement (MSA). It is specially designed for the high performance integrated duplex data link over a single optical fiber. BiDi SFP interfaces a network device mother board (for a switch, router or similar device) to a fiber optic or unshielded twisted pair networking cable. Nowadays, it is one of the most popular industry formats supported by many fiber optic component vendors.
You can read more on this here: https://medium.com/@teresahuangting/things-you-should-know-about-bidi-sfp-modules-eb001ced582e#28dd
I hope it helps.