Mycorrhiza is a community between fungi and plants. The root tips of the plant are connected to some hyphal tips of the fungus. This community has advantages for both sides: The fungus provides the plant with water and nutrient salts, while the plant transmits photosynthetic products to the fungus. Sometimes mycorrhiza communities are called three-part communities because many mycorrhiza fungi are also associated with certain bacteria.
Explanation for children: Mycorrhiza is a community between fungi and plants. Here the roots of the plant connect with the fungal "roots" of the fungi. The fungus provides the plant with water and nutrients and in return it receives sugar from the plant.