We can talk about fractions in terms of numerators and denominators.

The denominator is written below the line, or fraction bar, and is the number of equal parts that something (the whole) has been divided into. Our cake was divided into four equal portions, so the denominator is 4.

The numerator is written above the line, and is the quantity, or number, of those parts that we are interested in. We are looking at the three remaining portions of cake, so the numerator is 3.