The more you learn about tea, the more products you will find that call themselves a tea. However, all true teas come from the tea plant, the camellia senensis plant. It only grows in one part of the United States at the Charleston Tea Gardens, but almost all tea comes primarily from the five following countries: China, Japan, Taiwan, India, and Sri Lanka. Their climates are conducive to the success of the camellia senensis plant~higher altitudes, high moisture, etc. You can find more information here.
Herb teas are not teas at all, but tisanes, meaning they are another plant brewed in very hot to boiling water to release a characteristic of the plant into the water. Our grocery and health food stores are filled with herb tisanes sold as teas, when they contain no tea in them at all. Black, oolong, green, and white teas are all made from the same plant, but oxidized for a different length of time (or in the case of white tea, not at all).
Many people are still jittery (pun intended) about the caffeine in tea, despite the fact that a cup of black tea holds 1/3 the caffeine of the same cup of coffee. Therefore, when planning a tea party, it’s a good idea to plan to serve two teas, including one tisane. Someone may ask for no caffeine, and you’ll be prepared.
Two other options include serving a rooibos tisane, available in every imaginable flavor, or naturally decaffeinating the tea. Your call. However, it is still primarily the case that those who avoid all caffeine are looking for an herb tisane to drink.