Multiplexers or “mux” are electronic devices used to take multiple inputs and select or choose which one of the inputs is passed through to the output of the device. A multiplexer can be as simple as having to inputs, one output, and one select line. If a logic one is present on the select line, it might choose input A that would be passed to the output.  If the select line had a logic zero, then it would then select input B to be passed through to the output of the mux.

In today’s electronics where systems have wide data busses, multiplexers are used throughout electronics, to help which housekeeping and of several different groups of data. They can almost take on the behavior of stoplight, where they can control that gets to go through. Multiplexers are used to help improve the amount of data throughput in digital systems, as they are efficient and handling large quantities of data traffic. 

A multiplexer in its simplest form is a switch — a switch that is a multiple input, single output device. When multiplexers are used, they are usually used together with a demultiplexer that takes single inputs and generates multiple outputs, the inverse of a traditional multiplexer.