what is meant by : "Written trail"?

Answer 1

Used to be referred to as a 'paper trail' but the current trend toward email has changed it.

It refers to being able to provide full documentation as to why something was done the way it was done and who ordered it to be done that way. It is protection for those who followed the direction of their superiors and auditors will require such things for purchases and major business decisions. In the US the new laws since ENRON have been put in place to insure the documentation is made and kept available.