The short answer
Tea is the leaf of one plant, Camellia sinensis. Everything else infused in hot water — chamomile, peppermint, rooibos, ginger — is a different plant with different chemistry, and the accurate word is tisane or infusion. 'Herbal tea' is the common term and it will not go away, but the distinction underneath it is real and worth holding on to.
Why the distinction matters in practice
Tea has a characteristic set of compounds: caffeine, catechins, theanine. Almost no botanical shares them. That means the brewing advice does not transfer — most infusions tolerate boiling water and a long steep in a way green tea never will — and it means a claim about tea says nothing about chamomile, and the reverse.
Caffeine is the exception people get wrong
Herbal infusions are usually caffeine-free, and 'usually' is doing real work. Yerba mate contains caffeine. Cacao husk contains caffeine and theobromine. Guayusa and guarana contain caffeine. If a caffeine-free drink is the requirement, the plant has to be checked rather than the category assumed.
What one is made of
A single plant part, most often: a flower head, a leaf, a root, a bark, a seed or a roasted grain. Commercial blends are usually several, and the ingredient order is worth reading — a great many fruit infusions are mostly dried apple with the named fruit some way down the list.
What TeaHQ does and does not say about them
This site describes what a botanical is, where it came from, how it is produced and what people do with it. It does not say what any of them does to a person. That is a different kind of claim, it needs a different kind of evidence, and TeaHQ holds it behind a review that has not been completed.