first of all, it states that a kohen is prohibited from marring a zonah, are there any exceptions to this rule. also what would happen to the children born from this union, if the father(kohen) was unaware of this eventuality(that the mother was a zonah)
yehudah, Gibraltar
This is what we wrote in the Background to the Daf:
(a) The Torah prohibits a Kohen from marrying a Zonah, with an Isur Lav (Vayikra 21:14). A Zonah is generally defined as a woman who had relations with a man out of wedlock. However, the Tana'im argue about the exact definition of who is a Zonah.
1. Some say that a Zonah is any woman who is unable to have children, since it is not the manner for men to marry such a woman. She is prohibited to a Kohen whether she actually had relations with a man out of wedlock or not.
2. Some say that a Zonah is any woman who had relations with a man out of wedlock, i.e. without Kidushin, or, according to others, any woman who made herself available for all (without Kidushin).
3. Others say that the only woman who is considered a Zonah is an "Eshes Ish," a woman who committed adultery.
4. The Chachamim say that a Zonah is a woman who had relations with a man to whom she is prohibited (Yevamos 61b).
(b) The Halachah follows the Chachamim, who say that a Zonah is a woman (at least three years of age) who had relations with a man to whom she is prohibited.
Accordingly, a woman is only considered a Zonah and prohibited to a Kohen if she had relations with a man whom she is Halachically prohibited from marrying. A child born from such a union (regardless of whether the father was aware or not) is considered a "Chalal", one who is unfit to serve as (or marry) a Kohen. However, such a child may marry any other Jew.
Y. Shaw