Technically, a university offers graduate degrees beyond the standard 4-year college bachelor's degree. Examples would be a Ph.D. or Masters Degree. A college will typically offer only 2-year, 4-year, and/or associates degrees. A lot of institutions that are mostly colleges, however, call themselves universities, and some colleges offer a few masters degrees, so there isn't necessarily a sharp boundary. Sometimes a college that originally offered no advanced degrees decides to begin doing so, but keeps "college" in its name. As indicated in other answers, a university is usually--though not always--larger than a college because it tends to take more resources to offer advanced degrees.