Basically, an Improper fraction is a fraction where the numerator (top number) is larger than the denominator (bottom number). It also means that its not simplified into a mixed number.
(For future reference, a mixed number is a number that contains a whole number (number on the left of a fraction) and of course a fraction)
I really hope this helps and I'm sorry to hear this problem you're having with your teacher. I wish you the best of luck and know that the brainly community is here to help whenever you have questions.