Probiotics are beneficial, "friendly" live bacteria and yeasts that enhance gut health by restoring microbiome balance, aiding digestion, reducing inflammation, and strengthening the gut barrier. Key sources include fermented foods—yogurt, kefir, sauerkraut, kimchi, and miso—as well as supplements, particularly beneficial for easing IBS symptoms, constipation, diarrhea, and antibiotic-induced imbalances.