Mushroom refers to the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground on soil or its food source.
The term "mushroom" also has several other meanings:
1. To grow or spread rapidly like a mushroom
2. A mushroom-shaped cloud from a nuclear explosion
3. In slang, something that appears suddenly and spreads quickly
4. A type of hat with a wide brim (mushroom hat)