Nutrients that change the composition of gut microbiota by providing “food” that promotes good bacteria growth. It’s mainly dietary fibre, like that you find in fruits, vegetables, and whole grains.
The gut microbes themselves. They strengthen the barrier against infection, and have antibacterial, immune-modulating, and anti-inflammatory aspects.
You find probiotics in foods like yogurt, kefir, kombucha, and kimchi.
The result of probiotic activity in the gut, like fermentation. As intestinal microbes consume prebiotic fibre, the result of that fermentation or consumption is what is known as postbiotics.