TBT is The Bell Tree, so it's an acronym for the site. However, many people used it as the name for the bells you earn by posting here as well (still do, although it really doesn't make sense.) Several users are trying to convert to using BTB, which would be more accurate meaning Bell Tree Bells. Sometimes you'll see TBTB, The Bell Tree Bells. c:
I remember the days last year when it was under 1mil, around when I joined TBT, and now it's skyrocketed to what it is now. :O Generally 4-6mil, but I have seen 8-15mil as well. I think it started to skyrocket when X & Y came out and now, wouldn't be surprised if it goes up more with ORAS coming out soon.
5 - 10 million is the RANGE. u have no idea what the actual distribution is. for all we know, all but one person could be selling for 10 million. the range is still 5 - 10 million but the average selling price is definitely not 7.5