1. <communications> (Or "multiple access") Combining several signals for transmission on some shared medium (e.g. a telephone wire). The signals are combined at the transmitter by a multiplexor (a "mux") and split up at the receiver by a demultiplexor. The communications channel may be shared between the independent signals in one of several different ways: time division multiplexing, frequency division multiplexing, or code division multiplexing.
If many inputs may be active simultaneously then the output bandwidth must be at least as great as the total bandwidth of all simultaneously active inputs. In this case the multiplexor is also known as a concentrator.
2. <storage> Writing multiple logical copies of data files. Placing the copies on totally separate paths to mirrored devices greatly reduces the probability of all copies being corrupt. Multiplexing differs from mirroring in that mirroring takes one data file and copies it to many devices, thus making it possible to copy a corrupt file many times. Multiplexing writes the data files to many places simultaneously; there is no "original" data file.