What is the difference between an herb and a spice? 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.