In the culinary arts, the word spice refers to any dried part of a plant, other than the leaves, used for seasoning and flavoring a recipe, but not used as the main ingredient. Why not the leaves? Because the green leafy parts of plants used in this way are considered herbs.
Every other part of the plant, including dried bark, roots, berries, seeds, twigs, or anything else that isn't the green leafy part, is considered a spice. Today, India is the world's largest consumer, producer, and exporter of spices.1? They even created the Indian Insitute of Spices Research devoted to the study of spices.
Examples of Spices