GCF or Greatest Common Factor or Lowest Common Multiple (LCM) is similar in the sense that they both allow people to work with big fractions without the help of a calculator. There is also a big difference between GCF and LCM. GCF is actually the greatest possible number that evenly divides every number present in the set. LCM or Lowest Common Multiple on the other hand is the lowest number that can be divided evenly by every other number present in the set.