You refer to "trade paper original" and "mass market." I don't know that I've ever heard the phrase "trade paper original."
Trade paper original, or TPO, is a book that's first published in paperback, but in the bigger size, not the small mass market size. Mass market size are the ones you see at the grocery stores, retail price $6.99.
TPO are bigger, just slightly smaller than a hardover, and retail for $12-$15 and up.
There are other offbeat sizes too, but don't worry about those.
Generally rights are divvied up as: hardcover (hc), trade paperback (tp) and mass market (mm).
Any of those sizes can be original if the book is published FIRST in that form.
This kind of information is useful and you can find a lot of it in one place in Writers' Market books. Even year old editions can be useful if you want to save dough. The contact info in them is outdated almost as soon as it's published....they asked for our updates for the 2007 edition in January of 2006 to give you an idea of lead time.