Microorganisms that live in the intestines, we all have them, they're good, and a lot of people try to take different probiotics to help adjust or change what's living in your intestines. Very important stuff. You really can't change it too much. The European Food Safety Authority has shown that there's really been no benefit to taking probiotics, but there's been some cases that show that it does help with irritable bowel or antibiotic associated diarrhea, because when you take an antibiotic actually it kills the stuff that made you sick but it also kills all the microorganisms that are in your intestines and that can cause diarrhea. Some repopulating the microorganisms with these probiotics can actually be beneficial to help prevent that diarrhea. So definitely if you take an antibiotic I would highly recommend it. You got irritable bowel, there's even been some studies that show it can help with immune function. These are all great things, but I don't think most people technically need it. As you age, sometimes the population in the GI tract changes with you and some people want to just put more back. So when you get yogurt, those live active cultures, that's what they're talking about.