Source : Free On-Line Dictionary of Computing

polylithism
     
         A property of a data-object that can exist in
        many shapes and sizes, but not simultaneously; which
        distinguishes it from a {union}.  It is often implemented as a
        set of {classes} (or structs) derived from a common {base
        class} (or with a common header, as in the case of structs),
        typically without any {method}s.
     
        It has been loosely described as {polymorphic} data.
     
        [Clarification?]
     
        (1996-01-07)