If you open up a dusty old Catholic book (and some new ones), there are usually some Latin terms printed on the inside cover or copyright page. These words could be any of the following: imprimatur, nihil obstator imprimi potest.
What do those terms mean, and why are they printed in so many Catholic books?
The short answer is that these terms reflect the permission given by a Church authority to publish a particular Catholic book.
The current Code of Canon Law explains that “Books or other writings dealing with questions of religion or morals cannot be exhibited, sold, or distributed in churches or oratories unless they have been published with the permission of competent ecclesiastical authority or approved by it subsequently” (Can. 827 §4).