Portobello are mature brown or white agaricus bisporus mushrooms. They can be used in plant-based recipes as hamburger patties, you can even use them as buns.
Mushrooms are the fleshy fruiting body of a fungus. They grow above ground, soil or from a food source. UV ray-treated (due to both sunlight and articial UV light tech) mushrooms are a source of vitamin d2. Many mushrooms are poisonous, resembling certain edible species. Gathering mushrooms in the wild is risky for the inexperienced and should only be undertaken by persons knowledgeable in mushroom identification.