There are many different definitions to be found, but I think these explain the variations in quite simple terms:

Bulb - a central bud surrounded by a fleshy layer. The bulb serves as a store for nutrients as well as a reproductive structure.

Rhizome - a reproductive stem which grows horizontally underground, topped by shoots and with roots below. The stem also acts as a food store. Some rhizomes are edible, such as ginger, galangal and turmeric but common flowers are irises and various types of lily.

Tuber - a plump fleshy stem which divides for reproduction and stores food. Dahlias of all sorts of varieties are popular flowers but the humble potato is also a tuber.

Corm - A corm, as with the other types above, stores nutrients for the plant and also reproduces. It appears similar to a bulb but is usually smaller and harder in texture. Popular garden varieties are gladioli and crocuses.

You will see that all the different types of the generic "bulb" act as a food storage area for the plant and this is not only during the growing season but continues when the leaves die off and the plant becomes dormant. This is why all these perennials can be left in the ground as they all have their own survival system. Thus, when the weather conditions become suitable for growth, the plants reappear without human intervention. However, in order to maintain this annual reappearance, bulbs should be planted in well drained soil with plenty of moisture and, in most cases, sunshine. Soil that is too wet and retains a lot of moisture will cause the bulb to rot.

My experience of bulbs in Southern England is that snowdrops appear first, followed by crocuses then daffodils (in a sheltered spot) even while the weather is still frosty. Tulips, hyacinths and bluebells need more warmth so won't usually appear until spring is well under way and dahlias and gladioli will flower in the summer.

Planting time varies, depending on climate but most spring bulbs and rhizomes should be planted in late autumn or winter and summer flowering varieties in the spring.

Most bulbs enjoy full sunshine but if they are normally woodland plants, such as bluebells and snowdrops, then dappled shade will be more suitable, such as under deciduous trees. Planters, pots and window boxes are all suitable for growing bulbs too, as long as there is approximately three times their own height in depth of soil beneath the bulb. If you have problems with squirrels digging up and eating your bulbs, try planting them in a wire cage.

When the spring flowers are over, the leaves should be left to die off naturally as they provide the nutrients for the bulb to store for the following year, so don't cut them off or mow grass in which they are planted. If you want to reuse your tubs for summer bedding, you can, if you wish, dig up the bulbs complete and lay they out to dry in a warm dry place. When the leaves are quite dried up, they can be pulled off and the bulbs stored in a paper bag for replanting in the autumn. Unless your climate is very dry, tubers such as dahlias should be dug up when their foliage wilts with the first frosts as they are very prone to mould growth. Lay them out in seed trays or wooden boxes to dry and store in a dark dry place. The tubers will shrivel up, but don't worry, just before you want to replant them, remove them from the dark, sprinkle with a little compost and water very sparingly. You will notice that the tubers become plumb again and green shoots start appearing and this is when you can plant them out again as long as the danger of frost is past.

There are lots of varieties of all the above-mentioned plants to be found in garden centres but if you want some really exotic and exciting types, mail order companies have done fantastic work developing some real beauties!