Fungi (singular fungus) are creatures belonging to kingdom Fungi (like mushrooms, molds and yeasts) or extraterrestrial creatures similar to fungi in nature and lifestyle. Fungal organisms are difficult to classify as either fauna or flora, though they have been included among flora by some authors. Genetically, Earth fungi are more closely related to Earth animals than to Earth plants. Additionally, some fungi are microscopic in size, and thus can be classified as microorganisms.

They are usually saprophagous and digest food externally, but there may be exceptions. Although there are fungi which are parasites or even predators, most will be generally regarded as vegetation.