i keep hearing the term trans box or T-box, forgive my ignorance but what is it?

It's a legal-size prepaid mailing envelope most commonly used for expediting loan packages. They always come in white and are practically impossible to rip. These T-Boxes are almost/always used by courrier route.

why are they called T boxes and why cant regular envelopes suffice? I am just curious as to why it is so common in the loan field

A full package loan file can be pretty big, and they are full of the customers personal information. Plus god forbid your loan package got wet from the rain the lender would just throw it away and ask you to send another. It is always worth the extra money to be sure you can keep track of your file going to the lender thru UPS/FED EX. Most lenders will accept scanned files or faxed, but there are some old fashioned lenders that havent caught up with the times.

The common excuse from underwriters is "I never recieved the package" or "we didn't get your fax". We all know it's a lie, but you just have to have something to keep them honest.

got it, thank you