Source : WordNet®

fudge factor
     n : a quantity that is added or subtracted in order to increase
         the accuracy of a scientific measure [syn: {correction}]

Source : Free On-Line Dictionary of Computing

fudge factor
     
        A value or parameter that is varied in an ad hoc way to
        produce the desired result.  The terms "tolerance" and {slop}
        are also used, though these usually indicate a one-sided
        leeway, such as a buffer that is made larger than necessary
        because one isn't sure exactly how large it needs to be, and
        it is better to waste a little space than to lose completely
        for not having enough.  A fudge factor, on the other hand, can
        often be tweaked in more than one direction.  A good example
        is the "fuzz" typically allowed in {floating-point}
        calculations: two numbers being compared for equality must be
        allowed to differ by a small amount; if that amount is too
        small, a computation may never terminate, while if it is too
        large, results will be needlessly inaccurate.  Fudge factors
        are frequently adjusted incorrectly by programmers who don't
        fully understand their import.  See also {coefficient of X}.