Yours, Etc.: Origins and Uses of 8 Sign-Offs
The smallest number that can be divided evenly into two other numbers (see common denominator). When fractions with different denominators are added together, their denominators have to be made the same; thus, fractions with denominators of nine and twelve have thirty-six as a lowest common denominator. Seventy-two and 108 are also common denominators for fractions with denominators of nine and twelve, but thirty-six is the lowest.
Note: The term lowest common denominator is often used to indicate a lowering of quality resulting from a desire to find common ground for many people: “This fall's TV programming finds the lowest common denominator of taste.”