The GCF, or greatest common factor, is the largest positive integer that divides each of two or more integers. It is also known as the greatest common divisor (GCD) or highest common factor (HCF). The GCF is often used to simplify fractions and is the largest factor that all the numbers share. There are different methods to find the GCF, including factoring, prime factorization, and division. The GCF is a commutative, associative, and multiplicative function. For example, the GCF of 12, 20, and 24 is 4, which is the largest factor that all three numbers share.