"Bring to a boil" refers to heating a liquid until bubbles break the surface (212 degrees F for water at sea level). The term also means to cook food in a boiling liquid. A full rolling boil is one that cannot be dissipated by stirring.
From The Food Lover's Companion, Fourth edition by Sharon Tyler Herbst and Ron Herbst. Copyright © 2007, 2001, 1995, 1990 by Barron's Educational Series, Inc.