Fluorescence provides a quantitative measure of the "whiteness" of the diamond such that in general a diamond with zero or very faint fluorescence is preferred. Diamonds may also exhibit varying degrees of 'milkiness' or very slight brown or green colouration. These are more advanced grading filters but nevertheless have an influence on the diamond's value.
The symmetry refers to the balance and alignment of the stone once cut and attests to it's brilliance and scinitillation in terms of the light entering and reflecting from the diamond.
The polish refers to the finish of each facet of the diamond such that an absence of tiny scratches or burns will result in an 'excellent' grading.