Lowest terms basically means that the fraction/ mixed number is in simplest form. Which means it can't be divided by anything to get a lower number for both the numerator and denominator because they don't have anymore factors that they share. For example, if I wanted to simplify the fraction, 4/8. I would divide by 4 on both the top and bottom since that is their greatest common factor.
4 ➗ 4=1
8 ➗4=2
1/2 would be the "lowest terms" of 4/8 since 1 and 2 don't have any common factors except 1.