For example,
$$\frac{\text{part}}{\text{whole}} \cdot 100 = \text{percentage}$$
Example
$$\frac{1}{4} \cdot 100 \%$$
What is the quantity $\frac{\text{part}}{\text{whole}}$ called?
From the above example, it would yield $0.25$; what is the mathematical term for this quantity?
Your specific example seems to be a rational number (fraction) between $0$ and $1$.
So the term Portion (a private case of Fraction) would probably be the most appropriate.