Encoders are devices that take in one input, or a set of inputs, and output a digital code, which is usually a binary number. They are used to convert data in one format to another format, or to map one set of digital inputs to another set of digital outputs.
Decoders are the opposite of encoders, taking a digital code and outputting one or more analog or digital signals. They are used to turn digital input signals into something we can recognize like sound or light.
Multiplexers (also known as Multiplexers, Muxes, or MUXs) are devices used to combine two or more input signals into one output signal. A multiplexer allows multiple signals to be sent over the same wire or cable, which can save on the number of wires and cables needed for a given application.
Demultiplexers (also known as DEMUXs or DMUXs) are the opposite of multiplexers. They take one input signal and allow it to be split into multiple output signals, allowing it to be sent out to multiple destinations. Demultiplexers are commonly used in communication systems, allowing one signal to be sent to multiple locations.