Before us is Mishnah 4 in chapter 8 of Maseches Nedarim, which deals with vows that a person makes contingent on the seasons of summer and harvest, and with the question of how we determine the point in time the one who vowed had in mind.
"Ad hakayitz" and "ad sheyihei hakayitz":
One who says "ad hakayitz" - until the summer - or "ad sheyihei hakayitz" - until the summer arrives: as was explained in the previous mishnah, when the time period is undefined, such as the summer, then even when a person uses the wording "until it arrives," he means only the beginning of that period.
And what is "summer" in this context? It does not refer to the summer season in its plain sense, but to the period in which the figs ripen, are picked and made ready. Therefore one who says "until the summer arrives" means "ad sheyaschilu ha'am lehachnis bikelalos" - until the time when people begin to place the picked figs into the baskets.
"Ad sheya'avor hakayitz":
One who says "ad sheya'avor hakayitz" - until the summer passes: here there is no room for doubt about his intention. Even though we are dealing with an undefined span of time, it is entirely clear that he means until the summer's end. The only question is which moment is considered the end of the summer, and about this the mishnah says: "ad sheyekaplu hamaktzu'os" - until the maktzu'os are folded up.
And what are the "maktzu'os"? There are two opinions:
Knives: Some say the reference is to the special knives used for cutting figs, with which they would cut them in the process of preparing fig cakes. Once these knives are folded up and put away, the season's work is finished - and that is "until the summer passes."
Mats: Others explain that the reference is not to knives but to a kind of mat on which they would dry the figs. Once the mats are folded up, it is a sign that the summer has passed.
"Ad hakatzir":
Another case in the mishnah: one who says "ad hakatzir" - until the harvest. The mishnah says that he means "ad sheyaschilu ha'am liktzor ketzir chitin" - until people begin to reap the wheat harvest - and not the barley harvest. That is, one who uses the general term "harvest" means the wheat harvest and not the barley harvest.
"Hakol lefi mekom nidro":
But the mishnah qualifies this ruling and states: "hakol lefi mekom nidro" - everything goes according to the place where he made his vow. Even though the usual standard is the wheat harvest, the matter depends on the location of the one who vowed:
"Im hayah bahar": If he was in the hill country, the matter is determined according to what takes place in the mountainous region.
"Baviká'ah": If he was in the valley, the matter is determined according to the valley.
It emerges that even though the mishnah said that "harvest" refers to one particular type of harvest, in practice everything is determined according to the place.
In summary: In this mishnah we learned that "until the summer" and "until the summer arrives" mean the beginning of bringing in the figs in baskets; "until the summer passes" means the folding up of the maktzu'os - either the knives or the mats; "until the harvest" means the beginning of the wheat harvest and not the barley harvest - and everything goes according to the place where he made his vow, whether in the hill country or in the valley.