SFP fiber transceivers can support half-duplex SFP or full-duplex SFP, or in some cases, both. Duplex refers to the direction that data travels. Full duplex and half duplex are two different transmission methods in networking.
Full duplex is frequently compared to communication as occurs in a telephone and half duplex to communicating using a walkie talkie. Full duplex specifies the ability to perform the dual task of sending and receiving data. It can multitask and avoids collisions by maintaining separate frequencies for the data that it sends and the data that it receives.
Half duplex, on the other hand, has to switch between sending and receiving data. Half-duplex devices can be either sending data or receiving data, but they cannot do both.