Bulbs: Daffodil and tulip are bulbs. Bulbs are condensed stems, in which swollen succulent leaves form the main body of the bulb, and it is in these swollen leaves of the bulb that the plant stores food.
Corms: Crocus or gladiolus are corms. Corms are swollen stems, but the stems act as the storage organ.
Tubers: Potatoes and Dahlia are tubers. Tubers are simpler, are are either a swollen root (as in dahlia) or swollen underground stem (as with potatoes).
Some plants are difficult to class, such as cyclamen, which are half-way between corm and tuber.