If the fraction has been simplified then there is no such number.
How many parts of the total there are, the bottom number tells the total number of parts.
How many parts are available out of the total number of parts.
In the original fraction it is the denominator but if the fraction has been simplified you are out of luck. There is no way to recover the value of the total (nor the parts) from a simplified fraction.
The denominator (bottom number) of the fraction.
That would be the denominator or bottom number of a fraction. This tells you the overall size of the fraction, while the numerator or top number, indicates how many parts of the fraction are there (i.e. 1/9 means you have one of 9 total parts).
the total number of parts in a fraction
There are three parts to a fraction, there is the numerator (the top number), the denominator (the bottom number) and the vinculum (the line in the middle which means 'divide by'-
The bottom number.
How many parts out of the total number of parts are present.