A demultiplexer (DEMUX) is a digital switch that takes a single input signal and routes it to one of multiple outputs based on select lines. It has one input and 2^N outputs, where N is the number of select lines. Common types include 1-to-2, 1-to-4, and 1-to-8 DEMUXs. The document provides block diagrams and truth tables demonstrating how a 1-line input is routed to one of eight outputs depending on the states of the three select lines. Typical applications of DEMUXs include routing a single data source like a printer to the appropriate destination like a color or B/W printer.