Quite often the term ‘bulb’ is used to collectively describe bulbs, corms, tubers, and rhizomes. They all do the same thing; store food for the plant to use when it starts to grow. But in reality, there are some major differences.
Bulbs have many fleshy layers inside with a miniature flower in the middle. A good example is a daffodil.
Corms have a more solid feeling exterior and no internal fleshy layers. Unlike a bulb, after flowering, a corm is completely empty. However, during its growth cycle, it forms a completely new corm on top of the old one to replace it. Crocuses grow from corms.
Tubers have growing points all over it, all of which can grow into roots or shoots. Potato is a great example of a tuber.
On the other hand, a tuberous root starts life as a swollen root that can only grow from one end, like dahlias.
Rhizomes are a fleshy underground stem that grows horizontally, either underground or at ground level. Like tubers, these have many growing points. Bearded irises are grown from rhizomes.