de·cod·er / diˈkōdər/ • n. a person or thing that analyzes and interprets something, in particular: ∎  an electronic device for analyzing the information components of an audio or visual signal and feeding them to separate amplifier channels. ∎  an electronic device that converts a coded signal into one that can be used by other equipment.

decoder
1. The means by which a decoding process is effected (see code). It may be implemented in hardware or software, the process being algorithmic in nature.

2. See decoder/demultiplexer.

decoder In telecommunications and electronics, a device that converts the information content of a signal into a more intelligible form. In a satellite-television receiver, it decodes encrypted signals; in a colour television, it separates the red, blue and green components.