It is a figure of speech known as a synechdoche. For example, you might say "wheels" to mean a car or "bread" to represent food of all sorts.
It is the numerator of a fraction which is above the denominator.
A fraction.
2.45 is a fraction and there is no way to represent it as a whole number. The whole part of it is 2.
A simple fraction represents a part of the whole.
9.81 is a mixed number and there is no way to represent it as a whole number. The whole part of it is 9.
It is the numerator of a fraction which is above the denominator.
A fraction.
810.4 is a fraction and there is no way to represent it as a whole number. The whole part of it is 810.
2.45 is a fraction and there is no way to represent it as a whole number. The whole part of it is 2.
synecdoche
A simple fraction represents a part of the whole.
19.304 is a mixed number and there is no way to represent it as a whole number. The whole part of it is 19.
418.971 is a mixed number and there is no way to represent it as a whole number. The whole part of it is 418.
16.25 is a mixed number and there is no way to represent it as a whole number. The whole part of it is 16.
6.1 is a mixed number and there is no way to represent it as a whole number. The whole part of it is 6.
0.0625 is a mixed number and there is no way to represent it as a whole number. The whole part of it is 0.
-3.5 is a mixed number and there is no way to represent it as a whole number. The whole part of it is -3.