Duplex

In communications, duplex means "two-way" when referring to communications channels.

• A simplex channel is a one-way channel.
• A half-duplex channel is one that can carry information in both directions, but cannot carry it in both directions at the same time.
• A full-duplex channel is a channel which can carry information in both directions at once.

These terms apply also to early PC sound cards. Most are now full-duplex.

Where channel access methods are used for dividing forward and reverse communication channels on the same physical communications medium, they are known as duplexing methods, such as:

• Time division duplex (TDD) is the application of Time division multiple access to separate outward and return signals
• Frequency division duplex (FDD) is the application of Frequency division multiple access to separate outward and return signals

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A duplex home is one in which there are two separate residences, usually side-by-side, but sometimes on two different floors. The former often looks like two houses put together, sharing a wall; the latter usually appears as a townhouse, but with two different entrances.