1. The problem is to understand the full meaning of the abbreviation GCD. 2. GCD stands for "Greatest Common Divisor". 3. It is a concept in mathematics, specifically in number theory and algebra. 4. The Greatest Common Divisor of two or more integers is the largest positive integer that divides each of the integers without leaving a remainder. 5. For example, the GCD of 12 and 18 is 6 because 6 is the largest number that divides both 12 and 18 exactly. 6. This concept is useful in simplifying fractions, finding common denominators, and solving problems involving divisibility.