Herbs and spices are often referred to together, and there is good reason for this. They are actually very similar to one another, and they are only distinguished by what part of the plant they are derived from.
While herbs are made from leafy green parts of a plant, spices are made from seeds, roots, bark, or other similar parts of a plant.
So what about oregano? Is oregano a spice or an herb?
Oregano is the dried leaf of the plant, so that makes it an herb.