There are eighteen types of organic  defects that can render an otherwise kosher animal non kosher. However, the halachah is that since most animals ARE assumed to be without defects, there is no need to do a post mortem to look for defects. Only if we happen to see it, must we check it out. However, in the third century, a rabbinic enactment was made, that we must check the lungs. Why? Two reasons are given. First, the lungs, unlike other organs, are subject to many common problems. Although a minority of animals have these problems, it comes close to being half. (Other defects might be 1 or 2 percent). Secondly, when the animal's chest is cut open in order to remove the viscera. the lungs are immediately visible, and therefore easy to check. Even after this enactment, however, if the lungs are lost (e.g., grabbed by a dog), the slaughtered animal is nevertheless assumed to be kosher. The primary problem with the lungs is adhesions. Fluids in and around the lungs often harden into string like connections with other parts of the lung, or with other organs. The adhesion themselves are not the problem. The problem would be that the adhesion often is formed where there is a hole in the lung. A hole would render the animal non kosher. Also, the adhesion may be in a place where it is fairly certain that it will eventually tear, thus insuring a fatal lung defect. In the latter case, the animal is already considered to be non kosher. In the former, we need to ascertain if there is already a hole. The adhesion would be carefully peeled off. The lung (or part of it) would be placed in water, with air being blown in. If it bubbles, we know that there is a hole, and the animal would be declared non kosher. if no bubbles, the animal is kosher. In some places, however, where meat was plentiful, the custom became to not check for holes, but to consider the animal as non kosher if an adhesion was found. This is known as "glatt" (smooth, without question) kosher, "Halak" in Hebrew. Glatt has become almost universal in the U.S. and most other countries since about 1990. The term is often used loosely to mean "strictly kosher". Therefore, one will find even dairy restaurants declaring themselves "glatt"!  You will recall that in Ashkenazi tradition, custom trumps sources. The great Ashkenazi "voice" in the Shulchan Aruch is known as RAMA (Rabbi Moshe Isserles). He testifies that it is the accepted custom of Ashkenazi shochetim to consider an adhesion to be a problem only if it is white or yellow. Clear would never be an issue. Thus, an animal with clear adhesions would be called "glatt" even though it might be not kosher at all based on most classical sources. We thus have "Halak Beit Yosef" (glatt in accordance with the view of the author of the Shulchan Aruch, Rabbi Yosef Karo). This is now becoming accepted in many communities. Where I live, although there are few Sepharadim, many of the butcher shops only sell Halak Beit Yosef. The late sage, Rabbi Ovadia Yosef, ruled that although Halak Beit Yosef is the only one that should be used if possible, the others should be considered kosher also. So, at a communal meal, or at the home of an Ashkenazi, other kinds of kosher may be eaten by Sepharadim. Two objections to this system are cost, and the view of RAMBAM. In non-glatt , about 70% of the animals pass inspection. In glatt, about 30% pass. In Halak Beit Yosef, it comes out to about 15%. This greatly increases the price to the consumer. Moreover, even though RAMBAM is the single most esteemed halachist in Sepharadic tradition, with 70% of the Shulchan Aruch based on his rulings, it is often overlooked that he was extremely lenient about adhesions, unless it could be proven that a hole was already present. Although I am a fanatic about Sepharadi halachah, I will freely use non glatt meat, as long as it was properly supervised. Sadly (and scandalously), a campaign of delegitimazation has been going on against those remaining kashrut agencies that certify non glatt.  More next time.