I received an RC that says Please do not send mass market paperbacks.  What are they? 

Thanks,

Sharon

the smaller paperback books- the larger sized ones are called trade paperback . Mass market paperbacks are the kind of paperbacks you might see in the grocery store while trade sized paperbacks are about the same size as a hardcover. 

Hope that helps

Mass market = mmpb = standard 'pocket book' size paperback book.

Tradesize is larger

There's a new size that's similar to mmpb, only slightly taller - forgot the name tho.

Thank you!