academic auditor
person who, on his own initiative and without any duties, attends lessons or lectures in schools or universities
en-US/ˌækəˈdɛmɪk ˈɔdɪtɚ/
en-GB/ˌækəˈdɛmɪk ˈɔːdɪtə/
person who, on his own initiative and without any duties, attends lessons or lectures in schools or universities