common denominatorA number that is a multiple of all of the denominators in a group of fractions.
least common denominator(LCD) The least, or smallest, number that is a multiple of all the denominators in a group of fractions.
least common multiple(LCM) The least, or smallest, number that is a multiple of two or more numbers.
like denominatorsDenominators that are the same.
unlike denominators

Denominators that are different from each other.  For example the fractions  and  have different denominators, one denominator being 4 and the other denominator being 8.