According to Math is Fun, the meaning of simplest form is the numerator, or the top number of a fraction, and the denominator, or the bottom number of a fraction, cannot be reduced any further while still remaining a whole number. The concept of simplest form only applies to fractions.
Math is Fun explains that to reduce a fraction to its simplest form requires dividing the numerator and the denominator by the largest number that is evenly divisible. For example, a pie is divided into four parts. A boy eats two slices of the pie. The fraction used to represent the amount eaten is 2/4. The largest umber that can be evenly divided into 2 and 4 is 2. Dividing both the numerator and the denominator by 2 brings the fraction to its simplest form of 1/2.