CFU stands for the colony-forming unit, and this describes the cells that will be able to multiply to form a colony in probiotics.
Generally speaking, it is accepted that supplements should contain a minimum of 1 billion CFUs per strain. Supplements with lower numbers like this can be a way to ease into taking supplements, helping to avoid excessive gas or bloating.
The numbers of CFUs present in supplements can go as high as 50 billion. You should also check the labeling to ensure the CFUs are shelf-stable and not just alive during the manufacturing process.