Dolby

Well, Dolby labs has created quite a few different standards of audio
noise reduction and encoding.  Dolby isn't just noise reduction.  Here's
the most common buzzwords containing Dolby and their definition:

Dolby NR - a filter that can be applied at playback to reduce tape hiss
Dolby B - a filter that is applied at recording, and then again at playback
          to reduce hiss.  Fairly portable from one tape deck to another.
Dolby C - a dynamic filter this is applied at recording, and then again at
          playback to reduce hiss.  Not very portable from one deck to another.
Dolby Surround - a way of encoding sound on a recording, and then extracting
                 that sound during playback to produce a rear channel.  The
                 source material doesn't need to be encoded, but it usually
                 is to enhance the rear channel effect.
Dolby Pro Logic Surround - a way of encoding sound on a recording, and then
                 extracting that information during playback to produce five
                 distinct channels, RL, FL, C, FR, RR during playback.  Also
                 applies a steering function to enhance the directional effect.