My TBR is books owned. Many years ago I included books that I didn't own, but I quickly realized that if I hadn't bought the book, there was a 99.9% likelihood that I would never buy the book to read. If something interests me enough to want to read it, I buy it and add it to my TBR.
I do keep lists of books that have piqued my interest that I haven't bought and occasionally go through the lists to see if any of the listed books still interest me. If any do, I buy them and add them to my TBR; otherwise, they are simply scratched from the list. Rarely does a book on one of those lists get bought.
I find that my TBR pile grows much faster than I can read. The result is that I am likely to die long before I have significantly dented the TBR pile. Compounding my problem is that I tend to rank TBR books. What I mean is that if a book is really interesting to me and is definitely, without a doubt, one I want to and will read, I buy it in hardcover (assuming it is available in print). Those books that interest me enough to want to buy them but don't draw at me to read them ASAP, I tend to buy as ebooks.
For those interested in my TBR pile (although many of the books are no longer in the pile because I have read them since they were added to the pile), I publish a series on my An American Editor blog called
On Today's Bookshelf. There are currently 28 essays in that series.