without permission; without notice
absence from work without permission
truancy; absence without leave
staying out overnight without giving notice; spending night(s) away from home without permission (leave)
unauthorized reproduction; unauthorised reproduction; unauthorized copying; unauthorised copying
unauthorized use; unauthorized usage; use without permission
squatter; person who occupies a building or land without title or permission
unauthorized borrowing; borrowing without permission; unauthorized use; misappropriation; plagiarism