Niddah, Chapter 6, Mishnah 9. The final mishnayos of this chapter are a series of general rules, each one built on the word "kol," every case that carries one halachah also carries a second, though not always the other way around. Our Mishnah applies that pattern to the laws of the shemitah year, and to two of them in particular: biur, the removal of shemitah produce from the house, and the broader set of halachos that flow from kedushas shevi'is, the sanctity of the seventh year.
Some background is needed. Whatever grows by itself during the seventh year may not be worked and cultivated as in an ordinary year, yet a person is allowed to bring it indoors and eat from it. What is closed to him is treating the crop as a private supply, hoarding it away for future needs. His license is measured by what is going on outside: for as long as fruit of that kind is still to be had in the open, where a wild animal could wander over and feed on it, he too may hold it at home and eat it. But once that kind of fruit has run out beyond the fields, it may no longer remain in his possession indoors and has to be brought out. Taking it out in this way is the halachah of biur.
Now to the rule itself. The Mishnah states: "Kol sheyesh lo biur," every kind of produce that reaches a moment in the year when it has to be cleared from the house, because its species has run out in the open, is a fruit of which the Mishnah says "yesh lo shevi'is": it carries the entire remaining body of seventh-year law. Such fruit may not be traded or handled as merchandise, and while it is still on the tree or in the ground in one's own field, it must be left unowned and accessible to anyone who wishes to take. Biur, then, is never a lone obligation; wherever it takes hold, the other halachos of shemitah come with it.
The Mishnah now reverses the pairing: "Veyesh sheyesh lo shevi'is ve'ein lo biur," there is produce that is subject to shevi'is yet has no biur. Certain fruits carry the full sanctity of the seventh year, with every halachah that sanctity brings, and still the duty of clearing them from the house never attaches to them. That is the situation with a species that remains growing outdoors right through the year. Since such produce never actually runs out beyond the house, the condition that sets biur in motion never arrives. A person may hold this fruit at home for the entire year, and biur has nothing to do with it.
Here as well, then, the connection moves only one way. Wherever biur applies, the halachos of shevi'is are present alongside it, yet a fruit can bear the sanctity of the seventh year even though it will never have to be cleared out of the house at all.