I don't know about the biological definition of "herbal" but in practice herbal is used as a catch-all for tisanes, teas that are made without the Camellia sinensis (tea) plant. It's not a hard rule, e.g. rooibos teas are generally listed separately from herbals.
In any case, there are a lot of different herbals and the perfect water temperature might be different for all of them. When I drink herbals (rarely) I just use boiling water.
In any case, there are a lot of different herbals and the perfect water temperature might be different for all of them. When I drink herbals (rarely) I just use boiling water.