Herbs are plants grown for culinary, medicinal, or in some cases even spiritual value. The green, leafy part of the plant is typically used. General usage differs between culinary herbs and medicinal herbs. A medicinal herb may be a shrub or other woody plant, whereas a culinary herb is a non-woody plant. By contrast, spices are the seeds, berries, bark, root, fruit, or other parts of the plant, even leaves in some cases; although any of these, as well as any edible fruits or vegetables, may be considered "herbs" in medicinal or spiritual use. Culinary herbs are distinguished from vegetables in that they are used in small amounts and provide flavor (are spices) rather than substance to food.

The difference between herbs and spices is that spices come from the bark (cinnamon), root (ginger, onion, garlic), buds (cloves, saffron), seeds (yellow mustard, poppy, sesame), berry (black pepper), or the fruit (allspice, paprika) of tropical plants and trees. both can be used for culinary purposes but they come from different parts of the plant.

The most expensive spice in the world is saffron. heres what i found out about it:-

Saffron, botanical name crocus sativus, is the most expensive spice in the world. Derived from the dried stigmas of the purple saffron crocus, it takes anything from 70,000 to 250,000 flowers to make one pound of saffron. Moreover, the flowers have to be individually hand-picked in the autumn when fully open. Fortunately, only a little needs to be added to a dish to lend it colour and aroma; too much makes the food bitter and as the quotation from Culpeper (below) suggests, large quantities of it can be toxic.

Iranian Saffron from Khorasan Province in Eastern Iran Records detailing the use of saffron go back to ancient Egypt and Rome where it was used as a dye, in perfumes, and as a drug, as well as for culinary purposes. It reached China in the 7th century and spread through Europe in the Middle Ages. The town of Saffron Walden, where it was once grown commercially, takes its name from the plant. Now, however, most saffron is imported from Iran (southern Khorason) and Spain which are recognised as producing the best quality, but it can also be found in Egypt, Kashmir, Morocco and Turkey.