[tylan1]

The correct version is greatest common denominator. The lowest common denominator is usually 1.

[level3]

Maybe you're thinking of divisor instead of denominator?

[foota]

They're pretty much the same thing, some fractions are expressed as numerator/denominator

[level3]

Divisor in the sense of greatest common divisor is not the same as a denominator. More to the point, we may indeed care about greatest common divisors, but we also care about least common denominators (i.e. least common multiples)