A mushroom is just the fleshy, umbrella-shaped part of a fungus that pushes up above ground, while fungus is the much wider term for the whole organism, including the parts you never see. Picture an iceberg: the mushroom is the tip, and the fungus is everything below the surface too. Mushrooms are edible fungi you would put in a pan; fungus can also mean mold, yeast, or even an odd growth of tissue in a wound.
The core difference
Fungus is the broad living organism; mushroom is specifically its visible, umbrella-shaped fruiting body.
- fungus — a living organism such as a mold, mushroom, or yeast that lacks chlorophyll and gets its nutrients by absorption: the damp basement wall was covered in fungus.
- mushroom — the fleshy, umbrella-shaped fruiting body of certain fungi, often eaten as food: she fried the mushrooms in butter and garlic before adding them to the pasta.
How to tell them apart
Mushrooms are what a fungus produces above ground to spread its spores, in the same way an apple is what a tree produces to spread its seeds. The rest of the fungus, an underground network of threads, stays hidden and is not what people mean when they say mushroom.
The confusion mostly comes up around food and gardening: every mushroom is a fungus, but plenty of fungi, such as mold on bread or the yeast in dough, are never called mushrooms because they never form that umbrella-shaped fruiting body.
