Source : Free On-Line Dictionary of Computing

tail recursion optimisation
     
        (TRO) When the last thing a function or procedure does is to
        call itself, it is not necessary to retain the calling
        environment.  This is important when a procedure calls itself
        {recursive}ly many times for, without tail recursion
        optimisation, the environments of earlier invocations would
        fill up the memory only to be discarded when (if) the last
        call terminated.
     
        Tail recursion optimisation is a special case of {last call
        optimisation} but it allows the further optimisation that some
        arguments may be passed in situ, possibly in {register}s.  It
        allows recursive functions to be compiled into {iterative}
        loops.  See also {conversion to iteration}, {tail recursion
        modulo cons}.