A herb is a plant with useful properties that are not directly related to being eaten.
That said, a herb can be eaten, but will generally serve as a seasoning for food (or drink in some cases) rather than as a foodstuff in its own right, otherwise it may be prepared by a herbalist for use as a drug or for some other purpose - including driving off vermin, scenting places and goods or some industrial process (e.g. as a dye).
Game and Story Use
- Gathering herbs may be a useful source of income - or part of a fetch quest. It can also lead NPCs into places where they need rescuing from, or find interesting clues, either of which can supply your PCs with adventure hooks.
- Your PCs may want some culinary herbs to make their iron rations more edible.
- Where herbalism is a significant part of the rules, herbs may be important medical supplies.
- They may also act as green rocks to drive some useful power - a sort of poor man's version of a potion.
- A con artist could pass off pretty much anything as herbs, perhaps adding random chopped weeds to his preparations to give a veneer of medicine.
- If the herbs turn out to be poisonous or psychoactive, hilarity may ensure.