It's a form that I print out on 1 sheet of paper with a bar code. The Post Office then scans in the one bar code and it automatically updates all the packages I brought to the Post Office that they were presented at the counter right down to the minute. The Post Office can also do this if they took the time and scanned every package that had a delivery confirmation number on it. Some do many don't.

During the Holiday Season I sometimes have 15-20 packages and one bar code does it all. The scan form is available on USPS.COM but only if you print priority and above unfortunately. Still looking for the reason you can't print 1st class or media mail at USPS.COM.