In general use, herbs are any plants used for food, flavoring, medicine, or perfume. Culinary use typically distinguishes herbs from spices. Herbs refer to the leafy green parts of a plant (either fresh or dried), while a "spice" is a product from another part of the plant (usually dried), including seeds, berries, bark, roots and fruits.
Some plants contain phytochemicals that have effects on the body. There may be some effects when consumed in the small levels that typify culinary "spicing", and some herbs are toxic in larger quantities.