Usually a full time student takes 12 to 18 semester hours. If you fall below 12 semester hours you may affect your medical and/or car insurance (or your parents' medical and/or car insurance), your financial aid package (e.g., loans and/or scholarships), and your visa status (if you are an international student.)
Note, international students are required by law to be full-time students. For grad students this means that they must be taking at least 9 credits and for undergraduates 12 credits. Any questions related to visa situations should be taken to Mary Ann Brunner in the Center for International Education.The University is now mandated to let the INS know if a student goes below full-time.