Original: In electronics, a multiplexer or mux (occasionally the term muldex or muldemmuldem is also found, for a combination multiplexer-demultiplexer) is a device that performs multiplexing; it selects one of many analog or digital input signals and forwards the selected input into a single line.
Simplified: In electronics, a multiplexer or mux (occasionally the term mul-dex is also found, for a combination multiplexer-demultiplexer) is a device that selects one of many analog or digital input signals and outputs it into a single output line.