BiDi SFP and Compact SFP Transceivers(cSFP)

BiDi SFP and Compact SFP Transceivers(cSFP)

If you are a person working on fiber optic cables and connectors, you must have at least heard about BiDI SFP connectors and used it. Have you ever think that why are these modules are having a single port? Is that because it can do either of transmitting/receiving? If not, how does it differ from