Well, they have slightly different definitions that everybody pretty much accepts to be the same. At least, I think this is true.
A University contains several colleges. For example, I went to the University of Minnesota, which has The College of Education and Human Service Professions, The College of Liberal Arts, The College of Pharmacy, The Labovitz School of Business and Economics, The Medical School, The School of Fine Arts, and The Swenson College of Science and Engineering. I'm not sure where the differentiation between a school and a college comes in. They all looked the same to me.
(Technically, I went to the University of Minnesota Duluth, which is a campus of the U of M. UMD has its own colleges separate from other campuses.)
For the most part, when people say they're going to college, it means they're attending a university unless they're going to a smaller, community college which is all by itself, and isn't part of a University.
