In its simplified form, there is no such number.
This is the denominator, which is the bottom line of the fraction.
I'm not exactly sure what you mean, but the top number is called the numerator and the bottom number is called the denominator.
The denominator is the bottom number of the fraction. It tells how many parts in all. The numerator is the top number of the fraction which tells you the number of parts considered.
The denominator (bottom number) of a fraction tells you the number of equal parts (in a whole); The numerator (top number) of a fraction tells you how many of those parts. You have five parts out of 9 equal parts which is 5/9
If the fraction has been simplified, there is no such number.
How many parts are available out of the total number of parts.