Source : Free On-Line Dictionary of Computing

encoder
     
        1.  Any program, circuit or {algorithm}
        which {encode}s.
     
        Example usages: "{MPEG} encoder", "{NTSC} encoder",
        "{RealAudio} encoder".
     
        2.  A sensor or transducer for converting rotary
        motion or position to a series of electronic pulses.
     
        (1997-03-04)