Herbs have a variety of uses including culinary, medicinal, or in some cases even spiritual usage. General usage differs between culinary herbs and medicinal herbs. In medicinal or spiritual use any of the parts of the plant might be considered "herbs", including leaves, roots, flowers, seeds, resin, root bark, inner bark （cambium）, berries and sometimes the pericarp or other portions of the plant.
Culinary use of the term "herb" typically distinguishes between herbs, from the leafy green parts of a plant, and spices, from other parts of the plant, including seeds, berries, bark, root, fruit, and even occasionally dried leaves. Culinary herbs are distinguished from vegetables in that, like spices, they are used in small amounts and provide flavor rather than substance to food.
Some culinary herbs are shrubs （such as rosemary, Rosmarinus officinalis）, or trees （such as bay laurel, Laurus nobilis） – this contrasts with botanical herbs, which by definition cannot be woody plants. Some plants are used as both a spice and an herb, such as dill seed and dill weed or coriander seeds and coriander leaves.
Plants contain phytochemicals that have effects on the body. There may be some effects even when consumed in the small levels that typify culinary "spicing", and some herbs are toxic in larger quantities. For instance, some types of herbal extract, such as the extract of St. John's-wort （Hypericum perforatum） or of kava （Piper methysticum） can be used for medical purposes to relieve depression and stress. However, large amounts of these herbs may lead to poisoning, and should be used with caution. One herb-like substance, called Shilajit, may actually help lower blood glucose levels which is especially important for those suffering from diabetes. Herbs have long been used as the basis of traditional Chinese herbal medicine, with usage dating as far back as the first century CE.
Some herbs are used not only for culinary and medicinal purposes, but also for recreational purposes; one such herb is cannabis.
Herbs are used in many religions – such as in Christianity （myrrh （Commiphora myrrha）, ague root （Aletris farinosa） and frankincense （Boswellia spp）） and in the partially Christianized Anglo-Saxon pagan Nine Herbs Charm. In Hinduism a form of Basil called Tulsi is worshipped as a goddess for its medicinal value since the Vedic times. Many Hindus have a Tulsi plant in front of their houses.