Source : Webster's Revised Unabridged Dictionary (1913)

Portability \Port`a*bil"i*ty\, n.
   The quality or state of being portable; fitness to be
   carried.

Source : WordNet®

portability
     n : the quality of being light enough to be carried

Source : Free On-Line Dictionary of Computing

portability
     
         The ease with which a piece of
        software (or {file format}) can be "ported", i.e. made to run
        on a new {platform} and/or compile with a new {compiler}.
     
        The most important factor is the language in which the
        software is written and the most portable language is almost
        certainly {C} (though see {Vaxocentrism} for counterexamples).
        This is true in the sense that C compilers are available for
        most systems and are often the first compiler provided for a
        new system.  This has led several compiler writers to compile
        other languages to C code in order to benefit from its
        portability (as well as the quality of compilers available for
        it).
     
        The least portable type of language is obviously {assembly
        code} since it is specific to one particular (family of)
        {processor}(s).  It may be possible to translate mechanically
        from one assembly code (or even {machine code}) into another
        but this is not really portability.  At the other end of the
        scale would come {interpreted} or {semi-compiled} languages
        such as {LISP} or {Java} which rely on the availability of a
        portable {interpreter} or {virtual machine} written in a lower
        level language (often C for the reasons outlined above).
     
        The act or result of porting a program is called a "port".
        E.g. "I've nearly finished the {Pentium} port of my big bang
        simulation."
     
        Portability is also an attribute of {file formats} and depends
        on their adherence to {standards} (e.g. {ISO 8859}) or the
        availability of the relevant "viewing" software for different
        {platforms} (e.g. {PDF}).
     
        (1997-06-18)