1) Act of protest 2) Audit 3) Audit a class 4) Audit a course 5) Be a temp 6) Campus protest variety 7) Cause of some arrests 8) Certain kind of strike 9) Certain nonviolent protest 10) Certain protest 11) Civil disobedience 12) College protest 13) Common form of campus protest 14) Demonstrate in a way 
A sit-in or sit-down is a form of direct action that involves one or more people occupying an area for a protest, often to promote political, social, or economic change. ==Process== In sit-ins, protesters usually seat themselves at a strategic location (inside a restaurant, in a street to block it, in a government or corporate office, and so on). ...
a tactic of nonviolent civil disobedience. The demonstrators enter a business or a public place and remain seated until forcibly evicted or until ... [2 related articles]
A director may invite a group of the actors' friends to 'sit in' on a rehearsal. 
[v] - attend as a visitor 2. [v] - participate in an act of civil disobedience[n] - a form of civil disobedience in which demonstrators occupy seats and refuse to move
noun a form of civil disobedience in which demonstrators occupy seats and refuse to move