Source : Free On-Line Dictionary of Computing

signal-to-noise ratio
     
        1.  (SNR, "s/n ratio", "s:n ratio") "Signal"
        refers to useful information conveyed by some communications
        medium, and "noise" to anything else on that medium.  The
        ratio of these is usually expressed logarithmically, in
        {decibels}.
     
        2.  The term is often applied to {Usenet}
        newsgroups though figures are never given.  Here it is quite
        common to have more noise (inappropriate postings which
        contribute nothing) than signal (relevant, useful or
        interesting postings).  The signal gets {lost in the noise}
        when it becomes too much effort to try to find interesting
        articles among all the crud.  Posting "noise" is probably the
        worst breach of {netiquette} and is a waste of {bandwidth}.
     
        [{Jargon File}]
     
        (1996-01-29)