Source : Free On-Line Dictionary of Computing

Plain Old Telephone Service
     
         (POTS) The traditional voice service provided
        by phone companies, especially when opposed to data services.
     
        Note that the acronym POTS is sometimes expanded as "Plain Old
        Telephone System" in which sense it is synonymous to {Public
        Switched Telephone Network} but used somewhat derogatively.
     
        (1998-05-18)