What are "Mekachos"?
Rashi: It is merchandise. Malbim - they accepted to forbid commerce on Shabbos, even en though the Torah did not explicitly forbid this.
What is "Shever"?
Rashi: It is grain, like "ba'Shever Asher Hem Shoverim."
Ibn Ezra: It is wheat and barley.
What is "Yom Kadosh"?
Rashi: It is Yom Tov.
Why did they say "v'Nitosh Es Shenas ha'Shevi'is"?
Rashi: This is like it says "veha'Shevi'is Tishmetenah u'Netashtah." Malbim - this is unlike the opinion that Shemitah applies only when Yovel applies 1 - this is only when all (the majority) of Yisrael are on their land.
How will that opinion explain our verse?! Perhaps he holds that they accepted to observe Shemitah mid'Rabanan, even though mid'Oraisa they were exempt. (PF)
What is "Masa Chol Yad"?
Rashi: Any loan; we will cancel it in Shevi'is.
