decoder

a person who decodes messages or the like.

a device for decoding cryptograms, codes, or the like, as an electric or electronic apparatus that transforms arbitrary input signals into letters, words, etc.

Navigation. an electronic circuit designed to respond only to certain signals and to reject others.

Computers. a circuit designed to produce a single output when actuated by a certain combination of inputs.

Television. a box attached to a television set containing circuitry to unscramble encoded signals, as cable-television programs or closed captions, so that the signals can be displayed on the screen.