A drink made by steeping herbs, spices, and flowers in hot water is a tisane or herbal infusion. (While the word “tea” is often loosely used to describe any beverage made with the leaves of a plant, true “tea” is made only from Camellia sinensis.)
The FDA also recommends proceeding with caution if you're considering supplemented tea like Comfrey (could cause liver damage), Woodruff (acts as an anticoagulant), Ephedra (could affect heart rhythm), Lobelia (may cause breathing problems), and even chamomile (may cause allergic reactions.) And don't assume that herbal tea doesn't contain caffeine. If caffeine keeps you up at night, make sure your box of tea explicitly says "caffeine-free" or "decaffeinated."