GBIC stands for Gigabit interface convertor.
The first generation optical devices had static lasers built onto the print circuit of the router or switch which made them really inflexible to upgrade or change. The industry reaction to this issue was to create standardized shapes for transceivers.
The GBIC was the first standardized optical transceiver shape. It's been used by Cisco, Foundry, Juniper, Extreme and many others. The GBIC transceivers have a transceiving side (Tx) and a receiving side (Rx). The optic comes in 4 different versions: T, SX, LX, and ZX. The T version is with a RJ-45 connector and sold as WS-G5483. The SX version is for Multimode and the LX and ZX are working on Single mode. GBIC optics are not available with DOM/DDM, this is not implemented on this optic.