>Maybe I’m reinventing the wheel, but I did not know the answer to my question and I thought it might be good idea to spread the news.
I copy and paste the following information:
A Paperback is simply a book that has a glued spine and a paper or cardstock outer cover (called "wraps" or "wrapper"). In contrast, a hardback (until recently) would have a sewn binding and a cloth or paper covered "board" cover.
A Mass Market Paperback (MMPB) is the relatively small "pocket-sized" book that fits in a rack designed specifically for such books. These began in the 1930s and are the cheapest way to get a book out on the market. These are distributed the same way newspapers and magazines are. Typically the paper is of poor quality, readily yellowing over time. These books show up in regular book stores but also in nontraditional spots such as airports, drugstores, and magazine stands.
A Trade Paperback is a larger book, often the same size as the hardback original. Typically the paper is of better quality than in the MMPB. Sometimes, even the text on the pages is exactly the same as that of the hardback copy, especially if put out by the same publishing house. Their price is higher than that of an MMPB but less than a hardback.
An Oversized Paperback is also a Trade Paperback, simply a larger format book with a soft binding. Often the hardback edition is also an oversized book. There are specific terms booksellers have traditionally used to tell you the size of a book, such as quarto or folio, but many book buyers are not familiar with these terms today. This is why booksellers often include either the dimensions of a book or they state "oversized" in the description of the book.
An Academic Paperback is one released by a university press and which may have a cover made of heavy paper, not the glossy cardstock seen in MMPBs and most Trade Paperbacks. Traditionally, many buyers of these books would have them custom-bound if they intended to keep them for a long time.
Source: Askville by Amazon
A Crime is Afoot 
>You are not the only one to need guidance on this issue Jose Ignacio – I get confused by it all the time. I ordered one book recently that had its format listed as 'perfect paperback'. I shall look forward to receiving it to find out what is perfect about it.
>Thanks Bernadette. I'll be also interested to find out what does a 'perfect paperback' mean.
>Bernadette JFWIW here is what Askville has to say abour 'perfect paperback': http://askville.amazon.com/perfect-paperback-Amazon/AnswerViewer.do?requestId=1765050
>Interesting Jose Ignacio – I think from that information it's probably going to be similar to what we in Australia are used to as trade paperbacks – we don't tend to get a lot of those mass market ones with the very cheap paper like you see in the US and we also don't have a lot of hard covers these days.
>Thanks for this. I've been meaning to find out what they all are.
>Trade paperbacks are typically the size used for self-published books and POD (Print on Demand). I prefer this size (usually 5 1/2" x 8 1/2"). You are correct the paper is usually better quality. Mass market books are sold at discount stores and grocery stores (mass)Ann