A fraction is considered "proper" when the numerator represents a smaller part of the whole compared to the denominator, making it less than one whole unit. This comparison is done in two different ways depending on if it's a numerical fraction or a polynomial fraction.
For numerical fractions to be a proper fraction the absolute value of the numerator must be less than the absolute value of the denominator.
For polynomial fractions to be a proper fraction the degree of the numerator must be less than the degree of the denominator.