Dallas Baptist University describes credit hours as "the basic unit for college credit" and notes they often reflect an estimate for in-class time required each week. In short, universities assign a number of "hours" to each class they offer, then use these numbers to track your progress toward a degree or certificate of completion.
A semester is a unit of time commonly used in the educational system to denote half of an academic year. "Semester hours" are the credit hours for which a student has been registered during the course of a semester. For example, if a student is enrolled in five classes, and each class is awarded three credit hours, that student is enrolled in 15 credit hours for the semester.
Different universities and programs carry different requirements for graduation. In many cases, the total number of credit hours needed for a bachelor's degree will range between 115 and 125 hours. Check with your program's specific requirements. To complete a standard bachelor's degree in four years, at 120 total required hours, students need to fill 15 credit hours per semester for eight semesters. Additional certifications, such as a minors or graduate degrees, carry their own credit hour requirements.
For many universities, the number of credit hours required for "full-time student" status is 12 per semester. Maintaining this number will often affect a candidate's ability to receive financial aid. It is important to note that the number of credit hours a student takes will often affect the cost of his or her tuition. Be sure to check with your college or university to estimate fees associated with credit hours.