A unit fraction is a fraction with a numerator of 1. For example the fractions in the image below are unit fractions.
A unit fraction can be expressed as the sum of two equal unit fractions.
1/2 = 1/4 + 1/4
1/5 = 1/10 + 1/10
1/8 = 1/16 + 1/16
A unit fraction can also be expressed as the sum of two different unit fractions.
1/3 = 1/4 + 1/12
1/2 = 1/3 + 1/6
Any fractions can be written as the sum of unit fractions in multiple ways.
9/12 = 4/12 + 4/12 + 1/12 = 1/3 + 1/3 + 1/12
9/12 = 2/12 + 6/12 + 1/12 = 1/6 + 1/2 + 1/12