What is the difference between an herb and a spice?
I would think an herb is from a plant, but then I have no idea what specifically a spice is. Not being much of a cook, they all seem related to me, and I often hear them referred to them all as "herbs and spices".
From fooducate.com
The difference between the two is where they are obtained from a plant.
Herbs come from the leafy and green part of the plant.
Spices are parts of the plant other than the leafy bit such as the root, stem, bulb, bark or seeds.
Examples of herbs include basil, oregano, thyme, rosemary, parsley and mint.
From spice-racks.com
Herbs are obtained from the leaves of herbaceous (non-woody) plants.
Spices are obtained from roots, flowers, fruits, seeds or bark.
In some cases both a herb and spice may come from the same plant. Dill is an example of this.
In short, herbs are fresh and spices are dried, but it is not that simple. Most herbs are fresh plants, sometimes on the stem (like rosemary), sometimes not (like bay leaf). Spices are non-leaf plant parts, dried, and usually ground to a powder. Of course there are exceptions like cloves and star anise.
From Iowa State University in the US (your regional definitions may differ):
Herbs are obtained from the leaves of herbaceous (non-woody) plants. They are used for savory purposes in cooking [...]. Herbs originated from temperate climates such as Italy, France, and England. Herb also is a word used to define any herbaceous plant that dies down at the end of the growing season and may not refer to its culinary value at all.
Spices are obtained from roots, flowers, fruits, seeds, or bark. Spices are native to warm tropical climates and can be woody or herbaceous plants. Spices often are more potent and stronger flavored than herbs; as a result they typically are used in smaller amounts. Some spices are used not only to add taste, but also as a preservative.
Some plants are both herbs and spices. The leaves of Coriandrum sativum are the source of cilantro (herb) while coriander (spice) is from the plant's seeds. Dill is another example. The seeds are a spice while dill weed is an herb derived from the plant's stems and leaves.
Herb examples
Spice examples
I got taught that the difference was water vs. fat cooking.
Herbs are water-soluble, meaning their flavor is extracted through cooking with water.
Spices are fat-soluble. They need to be "bloomed" in oil, or cooking with fat, to extract their flavor.
