In electronics, a multiplexer (or mux) is a device that selects one of several analog or digital input signals and forwards the selected input into a single line. Amultiplexer of 2n inputs has n select lines, which are used to select which input line to send to the output. Conversely, a demultiplexer (or demux) is a device taking a single input signal and selecting one of many data-output-lines, which is connected to the single input. A multiplexer is often used with a complementary demultiplexer on the receiving end.
Multiplexer is used to gather all different signals into single unit where as de-multiplexer is used to distribute all the signals from a single unit.