A web search for "What is an herb?" yielded the following definition: "Any plant with leaves, seeds, or flowers used for flavoring, food, medicine, or perfume." Talk about a broad concept!
Lest you think of herbs -- based on this definition -- as "practical" plants only, let's introduce yet another element into the discussion. Our Guide to Herb Gardens, Amy Jeanroy, speaks rightly of "ornamental herbs." I, myself use plants ornamentally in my landscaping that I would regard as "herbs."
So what's going on here? Is there a way to stop the madness? Can we narrow the term "herb" down some so that the definition is more reasonably focused?
Well, taking on such a task in a thoroughgoing manner would be a bit much for a single blog post, but let me zero in on just one subcategory of herbs: those used for culinary purposes. I found an interesting treatment of the definition of herbs by Danilo Alfaro, About.com Guide to Culinary Arts.
Danilo makes an important distinction that narrows down the application of "herb." For his subject, he says that the term "refers to any green or leafy part of a plant used for seasoning and flavoring a recipe, but not used as the main ingredient." As an example, he contrasts spinach and lettuce with herbs such as basil and dill. The former are classified as vegetables, because they serve as food -- in and of themselves -- while the latter are used to season food.
Danilo continues with another distinction: namely, that between a "spice" and an "herb." Whereas herbs come mainly from the leaves of qualifying plants, spices are "pretty much anything else -- for instance, any dried bark, root, berry, seed, twig or other plant matter that is used to season or flavor a dish." He uses cinnamon as an example. Cinnamon, a spice that some of us think of mainly during the Christmas season, comes from the bark of a tree.