These are the small dried unopened buds from the tropical clove tree. The strong spiciness of cloves is used in Western cooking for adding to sweet things such as pies and cakes or in mulled drinks, as well as in pickles, for studding into baked hams or into onions to flavour savoury stews and sauces. Indian cooking tends to use them just in savoury dishes, particularly with rice and meat.
Cloves also add their slightly bitter taste to several spice mixes, including Chinese five spice, Indian garam masala and the French quatre épice.
They can be bought whole or ground and should be used sparingly as their flavour can easily overpower.