A "miut hamatzui" is a phrased used to express a case where because of a small concern that something exists, or might happened, or does happen that the halacha is affected by this. An example is if there is a certain type of "treifah" by a kosher animal that is found in a small amount therefore this must be checked after that animal is shechted.
However what is the amount of a "miut hamatzui"? What are the different opinions in this?
(I don't feel my explanation of a "miut hamaztui" is adequate enough however it's difficult for me to express in English. Perhaps someone can edit it.)