We begin chapter 9 of Maseches Shabbos, mishnah 1. This chapter deals with the laws of tying - making knots and untying them on Shabbos.
"Eilu kesharim shechayavin aleihen" - these are the types of knots for which one who ties them is liable for desecrating Shabbos on a Torah level.
"Kesher hagamalin u'kesher hasapanin" - the knot of the camel drivers and the knot of those who work with ships.
What are these knots?
The camel drivers' knot: those who led camels would pierce the camel's nose and tie a rope or strap through it, forming a sort of ring, tied tightly so that it would remain in place permanently.
The sailors' knot: the same was done on a ship - they would make a hole in the side of the ship, pass a strap or a strong rope through it, and tie a permanent knot there.
Both knots serve one purpose: to create a permanent ring to which another rope can be tied, in order to control the camel or the ship.
And just as one is liable for tying such a knot, so too is he liable for untying it. The source of this melachah is found in the work of the Mishkan: those who trapped the chilazon, whose dye was used for the techeiles, needed to tie and untie their nets in order to catch it.
The opinion of Rabbi Meir:
"Rabbi Meir omer: kol kesher she'atah yachol l'hatiro b'yad achas - ein atah chayav alav" - even though the one who tied it intended it to be a permanent knot, according to Rabbi Meir he is not liable for it. By its very nature, a knot that can be untied with one hand is not strong enough to be counted among the knots for which one is liable, and the intention that it be permanent does not change that fact - after all, it is a weak knot that comes undone with one hand.
In summary: in this mishnah we learned which knots carry liability from the Torah - the camel drivers' knot and the sailors' knot, which are strong permanent knots meant to remain in place and to serve for tying an additional rope; that the liability applies both to tying and to untying, just as it was in the work of the Mishkan among those who trapped the chilazon; and the opinion of Rabbi Meir, that any knot which can be untied with one hand is not included among the knots that carry liability, even if it was made with the intention that it be permanent.