common denominator

Denominator that is a common multiple of, and hence exactly divisible by, all the denominators of a set of fractions, and which therefore enables their sums or differences to be found.

For example, 2/3 and 3/4 can both be converted to equivalent fractions of denominator 12, 2/3 being equal to 8/12 and 3/4 to 9/12. Hence their sum is 17/12 and their difference is 1/12. The lowest common denominator (lcd) is the smallest common multiple of the denominators of a given set of fractions.