hall pass

A hall pass is a pass or token used in American and Canadian public schools to show that a student has been authorization to be out of his/her classroom while lessons are in progress. They are commonly issued to students if they need to visit the restroom, if they have been asked to run an errand for a faculty member, or if they need to see the school nurse. A student wishing to leave school for an off-site activity may also require a hall pass.
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Noun
1. written permission from a teacher for a student to be out the classroom and in the halls of the school
(hypernym) pass, laissez passer