According to the text, the “freshman fifteen” is

                                     The “Freshman Fifteen”

A freshman is a first-year college student. “Fifteen” refers to fifteen pounds – the fifteen pounds added to a student’s weight in his or her first year. There are a number of reasons why first-year university students gain weight; but it’s encouraging to know that freshmen don’t have to add these harmful fifteen pounds.

                                                             (Taken from Active Skills for Reading)

GLOSSARY pound – libra (unidade monetária e medida de peso equivalente a 454 gramas)