Emeritus is a title given to a professor, bishop or other person with an important office. The title says that these people, while still holding their title, no longer practice their function. Usually, this is done because of old age. Usually the emeritus is put after the official title of the person, as in Professor emeritus.
In the time of the Roman Empire, it was used for soldiers, to say that they no longer needed to serve in the army. That way, a Bishop emeritus no longer needs to take part in the celebration of the mass, but he is still able to perform confirmations or to ordain priests.
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