duplex

Sometimes referred to as "full duplex," it is a data transmission that takes place in two directions simultaneously. "Half duplex" allows transmission in two directions, but only one at a time. "Simplex" only allows transmission in one direction.

When used in reference to sound cards and Internet telephony, duplex means the ability to send and receive audio at the same time, as on a standard telephone. Some sound cards and systems require a special full duplex audio driver, software that's usually available from either the manufacturer of the sound card or the program itself.