Why a portfolio is called “your book”

I’ve traveled to many art schools, being asked to review senior student portfolios, and speak on professional practices in the design business, and the one thing I always notice is the lack of direction in student portfolios.Without senior level courses on portfolio preparation, or classes taught by those who have been out of the field too long to know current trends, it is confusing, and students are left with their own thoughts on what a client wants to see.