Duplex refers to the ability of a communications interface to pass data in both directions simultaneously.
A Full Duplex or FDX interface passes data in both directions at once, while a Half Duplex or HDX interface must wait for receive data to finish before transmitting, and vice versa. An FDX interface is twice as fast as an HDX interface.
Not all interfaces support FDX operation.
Please read this important note regarding certain differences between Media Converters and Switches.