Nedarim, Chapter 7, Mishnah 5. In this mishnah we will deal with the definitions of three vows: one who vows against a bed, one who vows against a city, and one who vows against a house. In each case the mishnah clarifies what is included in the wording of the vow and what remains outside it.
One who vows against a bed:
"HaNoder min hamitah - mutar b'dargash, divrei Rabbi Meir. VaChachamim omrim: hadargash bichlal hamitah" - regarding a person who vowed not to benefit from a bed, the Tannaim disagree about his status with respect to a dargash:
Rabbi Meir: he is permitted to use a dargash. The dargash was a kind of bed that served as a sort of footstool for climbing up onto the large bed, and therefore it is not included in the term "bed."
The Sages: the dargash is included in the category of a bed, and therefore it is forbidden to him.
"HaNoder min hadargash - mutar b'mitah" - one who vows against a dargash is permitted to use a bed according to all opinions, since everyone agrees that this specific term, which refers to the small bed or the raised bed, does not come to include an ordinary bed.
It is worth noting that the Gemara brings an additional explanation of the dargash: a kind of bed that served only as a sign of good fortune, and had no practical function at all.
One who vows against a city:
To understand the mishnah, two concepts in the definitions of a city must be introduced first:
The techum of the city: an area of two thousand cubits around the city, within which a person is permitted to walk on Shabbos.
The ibbur of the city: a smaller area outside the city, seventy and two thirds cubits (seventy cubits and four handbreadths) around the city, which also has a role in the laws of eruvin. Its name derives from the expression for a pregnant woman (ishah me'uberes) - just as she has a small protrusion extending from her body, so too the ibbur is a small protrusion extending from the city.
"HaNoder min ha'ir - mutar likanes l'techum shel ir, v'asur likanes la'ibbur" - one who vowed not to benefit from a city is permitted to enter its techum, that is, the area of two thousand cubits, but he is forbidden to enter its ibbur, the seventy and two thirds cubits adjacent to it, since that area is considered an actual part of the city.
One who vows against a house:
"Aval hanoder min habayis - asur min ha'agaf ulifnim" - in the case of a house, as opposed to a city, there is no outer area that is considered part of it, and the prohibition applies only from the agaf and inward. The agaf is the place against which the door of the house closes: in the middle of the doorway there is a small strip of wood that stops the door from continuing to swing open in the other direction. The doorway may have a certain width, and in the middle of it is that strip. Anything located outside that agaf is not considered part of the house, and therefore the one who took the vow is permitted to make use of that area.
In summary: in this mishnah we learned three definitions. Regarding a vow against a bed, Rabbi Meir and the Sages disagree whether a dargash is included in the category of a bed, whereas one who vows against a dargash is permitted to use a bed according to all opinions. Regarding a vow against a city, the techum is permitted and the ibbur is forbidden, because the ibbur is considered part of the city. And regarding a vow against a house, the prohibition is limited to the area from the agaf and inward alone.