It is simply a fraction with a numerator of 1.
We call that cross multiplying.
like fraction
numerator
The numerator.
fraction bar
A proper fraction.
A fraction in simplest form is one in which the only common factor of the numerator and denominator is 1.
a unit fraction
Denominator and Numerator
It is the numerator.
A proper fraction, ie: the numerator is smaller than the denominator so it is less than one.