A factor or a divisor is a number that will divide into another number evenly and leaving no remainder.
A common factor.
common factor
common factor
That would be called a "common factor" of the two (or more) numbers.
This is called a factor. Factors, by definition, are numbers you can multiply together to get another number, or a product.
Like 21? Prime numbers.
A factor.
factor
A factor.
common factor
Each number is called a factor. The answer is the product.
That's called the greatest common factor, or GCF.