The greatest common factor (GCF) is also called greatest common divisor, or highest common factor. For 2 or more numbers, the largest positive number that divides the given numbers without remainder is the GCF.
For 120 and 48, number 24 is the GCF. That is, 120/24 = 5 and 48/24 = 2
No number higher than 24 can divide both numbers and come up with a positive whole number.