Matthew Shiner is right, a portfolio could mean many things. I have noticed a couple trends at various job conferences, and interviews, however.
One is an 'edited' prompt book. and by this I mean you bring an intact prompt book, but only a few examples of each section, such as reports, sign in, daily's, weekly's, etc.
The other is the portfolio book. As in, it's set up like a prompt book, but each section might have stuff from different shows.
And of course, there's always the ever-present design/shop work portfolio.
Some schools do like to keep copies of whole books for their archives. My best advice would be to check with the school.
I hope this helps!