Nedarim, Chapter Two, Mishnah 4. The Mishnah opens with a general rule: "S'tam nedarim l'hachmir u'peirusham l'hakel" - unspecified vows are treated stringently, while their stated explanation is treated leniently. A person who makes a vow that can be understood in two ways - one in which the vow is valid and the object becomes forbidden to him, and another in which it is not a valid vow and the object remains permitted - if he vowed without specifying what he meant, we follow the stringent understanding and assume that he intended a valid vow.
But "peirusham l'hakel" - their stated explanation is treated leniently: when the one making the vow explains and clarifies what he meant, even though his words could have been understood stringently, we are lenient and say that according to the explanation he gave there is no vow here at all.
How so? The examples of the Mishnah:
"Harei alai k'vsar melach" or "k'yayin nesech" - one who says that this item shall be to him like salted meat or like wine poured out as a libation. If he meant "shel shamayim" - the meat of a sacrifice, which belongs to the realm of the consecrated, or wine poured as a libation on the altar - this is a vow and the object becomes forbidden, since this is an attachment to a sacrifice. If he meant the meat and wine of idolatry, it is permitted, for as we have mentioned, one must attach his vow to something forbidden by virtue of a vow, something that became forbidden through a person's statement and words, and not to something inherently forbidden, something that the Torah forbade on its own, such as pork. Idolatry is like pork: the Torah forbade it, and therefore attaching a vow to it does not create a valid vow. And if he vowed without specifying which of the two he meant, it is forbidden, following the stringent understanding.
"Harei alai k'cherem" - there are two types of cherem in the Torah. If he meant a cherem dedicated to Heaven, which is considered consecrated property belonging to the Temple, it takes effect and forbids the object, since this is an item that became forbidden through a person's statement. But if he meant the cherem of the kohanim, whose whole content is that the item is given to the kohanim and it has no inherent, intrinsic sanctity at all, it is permitted, for when one attaches his vow to something that has no sanctity, the item he attached to it also has no sanctity and has no power to become a vow. And if he vowed without specifying which cherem he meant, it forbids.
"Harei alai k'ma'aser" - if he meant the tithe of animals, whose law is that from the animals born in his flock that year he separates one out of every ten and brings it as a sacrifice in the Temple, it forbids, since its status is the status of a sacrifice. But if he meant the tithe of the threshing floor, which is given to the Levi, it is permitted, since it has no inherent sanctity and involves nothing more than an obligation to give it to the Levi. And if he vowed without specifying, it forbids, following the stringent understanding.
"Harei alai k'Terumah" - if he meant the Terumah of the chamber, it forbids. The Terumah of the chamber refers to the shekels collected from all of Israel for the communal sacrifices, which were gathered in a pile in the chamber; from there they would take and fill baskets from the pile, and the entire Terumah of the chamber was used to purchase sacrifices, and therefore it is considered something forbidden by virtue of a vow and the vow is valid. But if he meant the Terumah of the threshing floor, which is taken from the produce and given to the kohen, it is permitted, since, as we mentioned in the previous Mishnah, Terumah is something inherently forbidden, forbidden by the Torah itself. And if he did not specify which Terumah he meant, it is forbidden. These are the words of Rabbi Meir.
The view of Rabbi Yehudah - the unspecified case is determined by locale:
Rabbi Yehudah disagrees about how we determine the intention of one who says "Terumah" without specifying, and he makes it depend on where the person making the vow lives:
Unspecified Terumah in Yehudah - forbidden. In Yehudah, which is close to the Temple, the assumption is that he meant the Terumah of the chamber, which is something forbidden by virtue of a vow.
Unspecified Terumah in the Galilee - permitted. The assumption is that he meant the Terumah of the threshing floor, since "ein anshei haGalil makirin es terumas halishkah" - the people of the Galilee are not familiar with the Terumah of the chamber; being far from the Temple, they were not well versed in it, and it would not have entered their minds.
And so too with regard to cheramim: in Rabbi Meir's view, an unspecified cherem is forbidden, on the assumption that he meant a cherem of consecrated property. Rabbi Yehudah says that this too depends on locale:
Unspecified cheramim in Yehudah - permitted, since we assume that he meant the cherem of the kohanim.
Unspecified cheramim in the Galilee - forbidden, since the people of the Galilee are not familiar with the cherem that is given to the kohanim, and therefore they would always assume that a cherem of consecrated property was meant, and attaching a vow to it forbids the object.
In summary: in this Mishnah we learned the rule that "unspecified vows are treated stringently, while their stated explanation is treated leniently," and its application to four expressions: salted meat and libation wine, cherem, tithe and Terumah. In each of them, attaching a vow to something whose sanctity is inherent and stems from a person's statement forbids the object; attaching a vow to something forbidden by the Torah, or to something that involves nothing more than an obligation to give it to a kohen or a Levi, does not forbid it; and in an unspecified case we follow the stringent view. We also learned the dispute between Rabbi Meir and Rabbi Yehudah, in which Rabbi Yehudah holds that the meaning of an unspecified statement is determined by where the person making the vow lives and by how familiar the local people are with each concept.