Pesachim, Chapter Three, Mishnah 1. This mishnah deals with items that, although they are chametz, are not considered full chametz. This is not the type of chametz for which one is liable to kareis, the most severe punishment for eating chametz, because these types of chametz have features that prevent them from being considered true chametz.
Two groups are discussed in the mishnah:
The first group - a mixture containing chametz: four items, all of which are mixtures of chametz with other things, and for that reason they are not considered full chametz. Even so, the amount of chametz in the mixture - the proportion of actual chametz found in it - determines whether one who eats it is liable to lashes, even though he is not liable to kareis. If he ate a kezayis of chametz within the time of kedei achilas peras, he receives lashes. (Kedei achilas peras is the time it takes to eat half a loaf, and opinions differ as to its size: some say about three eggs, and some say about four eggs.)
The second group - chametz nukshah: three items that are hardened chametz, entirely unfit for eating.
It is worth noting a distinction in the wording of the mishnah: the four items that are mixtures of chametz all bear names with a geographic association, while the three items that are chametz nukshah are all linked to the names of tradesmen.
The mishnah opens: "Eilu ovrin baPesach" - these are the things that must be removed before Pesach, even though one is not liable to kareis for them:
"Kutach haBavli" - a dairy food made of whey, bread crumbs and salt.
"U'shechar haMadi" - the beer of Media, made from barley soaked in water.
"V'chometz haAdomi" - vinegar from Edom, which comes from wine into which barley is mixed.
"V'zeisom haMitzri" - a type of beer from Egypt, containing spices, a bit of salt, and barley as well.
These four kinds are associated with different places, and all of them are mixtures of actual chametz with other items.
The next group, as mentioned, consists of things that are chametz nukshah:
"Zoman shel tzaba'im" - water mixed with bran, used by dyers in the process of dyeing their items.
"Amilan shel tabachim" - a type of dough used in the cooking process, made from grain that grew to less than a third of its normal growth. It was used to cover pots in order to absorb some of the undesirable elements of the food.
"Kollan shel sofrim" - a type of glue made from flour.
These items, associated with tradesmen, are chametz nukshah - chametz that is entirely unfit for eating.
The dispute between Rabbi Eliezer and the Sages:
Rabbi Eliezer adds "aptachshis nashim" as well, which is a type of cosmetic used by women. Some have the version "aptifuli nashim," a different cosmetic used as a kind of hair remover. The halachic difference is that Rabbi Eliezer adds something that has both features at once: it is both chametz nukshah, entirely inedible, and also merely a mixture containing chametz. The other items listed as chametz nukshah were full chametz without any mixture, only that they were unfit for eating. The Sages disagree with Rabbi Eliezer and hold that something which is both chametz nukshah and a mixture need not be removed.
"Zeh haklal":
The mishnah concludes with an all-inclusive principle: "Kol shehu min dagan, harei zeh over baPesach" - anything that comes from the five species of grain must be removed on Pesach. And all of these items - "harei eilu b'azharah" - carry a Torah prohibition, and one who eats them transgresses the Torah's prohibition of chametz, "v'ein bahen kareis" - but no punishment of kareis is attached to them.
To summarize: in this mishnah we learned about chametz that is not full chametz, in two groups: four kinds of chametz mixtures named after places (kutach haBavli, shechar haMadi, chometz haAdomi and zeisom haMitzri), and three kinds of chametz nukshah named after tradesmen (zoman shel tzaba'im, amilan shel tabachim and kollan shel sofrim). We discussed the measure of kedei achilas peras regarding liability for lashes, the dispute between Rabbi Eliezer and the Sages about something that has both features at once, and the rule that anything which is a species of grain must be removed on Pesach - under a prohibition, but without kareis.