Censors of Books
Clerics, in practise always priests, appointed according to canon law by the bishop of a diocese to examine, before publication, those writings or other things that are to be submitted to ecclesiastical supervision.
The censors are to be chosen either from the secular or regular clergy.
Conditions of age, learning, and prudence are to be considered in naming them.
As a guarantee of fitness the censors, before entering upon their office, make a profession of faith before the bishop or his vicar-general.
In examining what is submitted to them, they must lay aside favoritism, and consider the teachings of the Church and the laws of sound morals in order to determine whether the things in question may be given to the public with safety.
In each case the censor must give his opinion in writing.
If his opinion is favorable, the permission to publish is granted.
The fact of the favorable view of the censor must be shown on the publication.
This is usually done by placing there the Latin words, Nihil obstat, meaning "Nothing hinders the publication," and the name of the censor.
Then follows the word, Imprimatur, the name of the local bishop or of his vicar, and the place and date of permission.
Chiefly works on religious subjects or those which have a bearing on religion are presented for censorship.
New Catholic Dictionary