Cinnamon is a powdered spice that can be made from the bark of a few different trees that fall under the genus Cinnamomum. Spices like cinnamon are made from the aromatic seeds, bark, flowers, and roots of plants that have been dried and crushed.
Oregano, however, is an herb derived from the herbaceous oregano plant. Herbs are leaves, and although most come from herbaceous plants (plants that lack woody stems), a few do come from woody plants, such as bay leaf. Basil, rosemary, and parsley are often found in a kitchen’s spice rack but actually qualify as herbs because they are aromatic leaves.