A regular language debate in my family that played out again at lunch:

I mention an herbal tea with mint and fennel.
"It's really a tisane, not tea."
"You know what I mean." (And I'm the English major!)

Camellia sinensis is the plant that is grown and picked at so many stages and elevations to create many grades of black tea or green tea, oolong, or white tea. Chai. (If you say "chai tea" it is tea tea, too much tea!) Tea being synonymous with the Camellia s. product. Herbal teas don't contain Camellia anything, so technically are a tisane or an infusion. They aren't made with tea leaves.

But it's too late for that argument to win. Packages around the world say "herbal tea" and note "no caffeine" and have no Camellia in them. The "brand" tea isn't a proprietary eponym like Kleenex or Bandaid or Xerox or Aspirin, tea these days means just about any cup of hot water in which leaves or herbs are soaked to create a drink that isn't coffee.

Off my soap box. :)