Is a Broadway preview an actual performance? (See below for more info)

As my username states, Rent is one of my favorite shows ever. So, being a rent head, when they put it back on Broadway, I immediately bought tickets. Now, the ticket says “promo”, and on the online schedule it says “Preview.” So I was just a tad bit confused as to if it is the real show or just a part of it or something. If anybody understands this and/or knows what I’m talking about, please explain this to me. Thank you!