An octrooi is a patent. Historically, octrooien were not just required to protect inventions, but also to enter into certain types of businesses, similar to what we’d call a permit today. An octrooi could also grant permission to publish a book in a certain area.
Octrooien can often be found in the records of the landlords or the government. They typically describe the type of permission that is granted and name the patentee.