A mushroom is the fleshy, spore-bearing structure of certain fungi that pops up from the ground or grows on trees. Most mushrooms have a stem and a cap, like a tiny umbrella. The cap protects the gills underneath, which release microscopic spores that spread to create new mushrooms.

Mushrooms aren't plants: they're fungi, which means they don't make their own food through photosynthesis like trees and flowers do. Instead, they absorb nutrients from dead leaves, rotting wood, or soil. Some mushrooms are delicious to eat, like the white button mushrooms you might see on pizza or the shiitake mushrooms used in stir-fry. But many mushrooms are poisonous, some deadly, so you should never eat a mushroom you find outside unless an expert has identified it as safe.

The word can also describe something that grows or appears suddenly and quickly. A new neighborhood might mushroom seemingly overnight as construction crews build house after house. Social media trends can mushroom across the internet in just hours. This meaning captures how actual mushrooms can appear almost magically after a rainstorm, growing from nearly invisible to full-sized in just a day or two.