Real Dictionary

teach-in
countable noun: A teach-in is a meeting, usually between students and teachers, with discussions on important and interesting topics. Teach-ins are not usually part of a formal academic course.

teach-in in American English
a special, extended meeting, as at a college or university, with lectures, discussion, and debate on a controversial issue, esp. such a meeting held to protest against some policy
noun: a prolonged period of lectures, speeches, etc., conducted without interruption by members of the faculty and invited guests at a college or university as a technique of social protest

teach-in in British English
noun: an informal conference, esp on a topical subject, usually held at a university or college and involving a panel of visiting speakers, lecturers, students, etc