Glatt kosher is often understood to mean extra-super kosher. People may say that someone eats glatt if they will only buy products with certain kashrut certifications, or go to restaurants supervised by a particular authority.
This is a misunderstanding. Glatt kosher refers to mammals (not chicken or cheese or cornflakes) that are kosher without needing to rely on a leniency of the Ramah (Rabbi Moshe Isserles). An animal with a perforated lung is treif, not kosher. Certain adhesions on the lung should be checked to make sure that there is no perforation. The Ramah authorised a way of checking that allows many more animals to be considered kosher. Glatt, Yiddish for “smooth”, refers to animals that do not have such adhesions on their lungs, removing the element of doubt.
Mehadrin, meaning “splendid”, is a more accurate term for “extra high standards of kashrut”. As with all stringencies, there are trade-offs and tensions between striving for religious excellence on the one hand, and potentially causing divisiveness on the other.
Rabbi Julian Sinclair