What are the most inclusive among all the common factor?
1 is a common factor for all integers.
All numbers have factors. Some numbers have some of the same factors as other numbers. These are known as common factors. When put in a list, the largest of these is known as the greatest common factor, or GCF. Some people refer to this as the highest common factor, or HCF. Calling it the most common factor would be confusing, since people tend to think of "most common" as something that happens frequently.