This Mishnah will talk about a rental of land that overlaps with the Shemitah year—the Shemitah year when we don't work the land of Eretz Yisrael, we don't plant, and we don't work whatsoever. The question becomes: if a person rented the field, does he count the Shemitah year as part of his term, as part of his rental, when he wouldn't be allowed to work the land?
The Mishnah describes the case. The Mishnah says: Somebody rents a field from his friend, and he has an agreement with him that he's going to rent the field for a seven-year period. That seven-year period is going to be for the price of 700 Zuz (coins). We say that Shevi'it (the seventh year) is Min HaMinyan: the Shemitah year is part of those seven years. Since the way he described it was Shavua Echad, quote-unquote, “one week,” which means one, seven-year period, that means it's seven years in a row, even though one of those years includes the Shemitah year, when he can't work whatsoever. It's included because he grouped and linked all of these years together by saying Shavua Echad, one seven-year period. So the Shemitah year would be part of that.
But if you rented it from him saying, “I'm renting the field for seven years, for 700 Zuz,” Ein HaShevi'it Min HaMinyan: the Shemitah year, the seventh year, would not be part of the seven years that he rented it for. In this situation, he was implying that he's renting it for seven years. The implication there is that these are seven years that he could use it. So, therefore, he would keep the field for seven years, besides the Shemitah year that he had it.