Audition refers to people who attend classes informally. Double degree refers to the second bachelor's degree and the second minor degree. A minor degree refers to studying a degree course in another major while studying this major, and obtaining a bachelor's degree in another subject after meeting all the requirements. Those who fail to meet the requirements for applying for a bachelor's degree can get a minor degree. I think the main difference between auditing and double major is that auditing has no diploma, and double major credits are enough to give a certificate. * * * In common, everyone can attend classes.