What does it mean to audit a course? An audit means that you have registered for a course for no credit, when that course is normally a for-credit class. Students may register for a course as an audit by gaining the authorization of the instructor and completing an ADD form with the Office of the Registrar by the last day of Registration. Individual instructors have different requirements for an audit. Some may merely require attendance; others may require written work. This decision belongs to the instructor.
Why would I audit a course?
For the joy of learning. Because you always wanted to take the course but can not "risk" the grade. Because you want to learn the material but do not have the time for all the coursework or exam preparation.