Probiotics are live microorganisms, primarily beneficial bacteria and yeast, that provide health benefits when consumed in adequate amounts. They are often referred to as "good" or "friendly" bacteria due to their role in maintaining a balanced gut microbiome. Probiotics can be found in a variety of foods, such as yogurt, kefir, sauerkraut, and kimchi, as well as in dietary supplements.

These microorganisms work by colonizing the intestines, competing with harmful bacteria, and producing substances that inhibit the growth of pathogens. There are many different strains of probiotics, each with unique properties and benefits. Common strains include Lactobacillus and Bifidobacterium, which are known for their effectiveness in promoting digestive health and enhancing immune function.