Tevul Yom טבול יום

Immersion is not the end of purification: until sunset a person is not yet fully pure. The Torah names the state plainly: "and the sun shall set and he shall be clean". The tractate works out what such a person renders impure and what he does not.

It turns out his impurity is the weakest of all: he spoils terumah and holy things but does not make ordinary food impure. A whole tractate is given to a single day in between—and in that one sees how the whole order is built: not "pure or impure" but a multitude of degrees.

Order: Tohorot. There is no Gemara in either Talmud—the tractate remained mishnah.