So what’s a “barre class?”

There’s a new challenge (new to me that is) to take 6 “barre classes” in 7 days. No explanation of what this is, no class category of “barre,” no search results when one searches for “barre,” no search results in this forum for the term “barre.” The concept appears not to exist anywhere except in the challenge.

So is it “do nothing for 6 of the next 7 days?” Or do “anything you want for 6 of the next 7 days?”

I can do that.