The Torah forbids eating hametz on Pesah; even having it in your house on the holiday is forbidden.
The third perek (chapter) of Massekhet Pesahim, which begins on our daf (page), examines a very basic question: what is the definition of hametz? From the Torah it is clear that bread or a direct leavening agent is considered hametz. What about food or drink that has a small amount of hametz in it – are they also forbidden on Pesah? Does something with hametz mixed in need to be searched out and destroyed before the holiday? What percentage of a given mixture need be hametz for it to be forbidden? How about a product that contains hametz, but is not intended to be eaten? Is it, too, considered hametz?
These are the types of questions with which our chapter grapples.
The first Mishnah teaches that food, drink and even paste made from flour or grain is considered hametz. The specific examples are Babylonian kutah, Median beer, Edomite vinegar, Egyptian zitom, dyers' broth (zoman), bakers’ well-worked dough and bookmakers' kolan, or glue (the Gemara refers to these as "the four countries and the three professions"). Rabbi Eliezer even includes women's cosmetics – apparently a type of depilatory cream used for removing hair.
The prohibition, however, is only on the level of a simple negative commandment, which does not carry the more severe punishment of karet (excision from the people of Israel) if it is eaten. Introducing these items, the Mishnah uses the term Elu Ovrin, an expression that is understood in a number of ways by the rishonim. Rashi understands it to mean that keeping these things in your house over Pesah leads you to be over – to transgress – the prohibition of bal yera'eh u'bal yimatzeh, of having hametz in your possession.
Rabbenu Hananel suggests that the expression should be understood to mean ma'avirim me'al ha-shulhan - that these things need to be removed from the table, i.e. that they cannot be eaten. According to Rabbenu Yehonatan it means that these things need bi'ur; that they need to be searched for and destroyed.