Chapter 11 of Maseches Nedarim opens by listing the vows that a husband may annul for his wife. The Mishnah states: "V'eilu nedarim shehu mefer" - these are the types of vows that a husband has the power to annul. The first category: "Devarim sheyesh bahem inui nefesh" - vows that cause her distress and affliction, that are physically hard for her to bear and bring her to hardship.
The examples in the Mishnah:
For each matter the Mishnah gives two examples - one of a vow and one of an oath, since a woman can forbid something to herself in either way, and in both cases the husband can annul:
"Im erchatz" - the Gemara explains that this is a vow: she forbids upon herself all future bathing if she bathes today.
"V'im lo erchatz" - here it is an oath: she swears that she will not bathe.
"Im etkashet" - a vow, that every adornment and piece of jewelry will be forbidden to her forever if she adorns herself today.
"Im lo etkashet" - an oath that she will not adorn herself at all.
All of these involve affliction of the soul, and therefore the husband may annul them.
The opinion of Rabbi Yosi:
Regarding these two examples Rabbi Yosi says: "Ein eilu nidrei inui nefesh" - these are not vows of affliction. His words apply to the vows only and not to the oaths, and his reasoning is that the whole issue is a single day, since the prohibition takes effect forever only if she bathes or adorns herself today. Refraining from bathing or from adorning herself for one day is not considered affliction in his view, and she can escape the vow simply by refraining from the act for one day alone. Of course, if she does transgress on that day and the matter becomes forbidden to her forever, that does constitute affliction even according to his opinion.
Annulment under the category of "matters between him and her":
The Gemara explains that even according to Rabbi Yosi, who holds that these are not vows of affliction, the husband may annul these vows on the strength of a different category - "devarim shebeino l'veinah," that is, matters that touch on the relationship between husband and wife.
What is the difference between the two forms of annulment?
A vow that involves affliction of the soul: a vow that is hard for her to endure and bear. When the husband annuls it, it is annulled with respect to everyone - and even if they divorce and she marries another man, the vow does not stand.
A vow that falls under matters between him and her: when the husband annuls it, the annulment is effective only as long as she is married to him. Its force is limited to the framework of their relationship alone, and it has no effect on her relationships with others.
In summary: in this Mishnah we learned about the vows a husband annuls - matters that involve affliction of the soul, whether expressed as a vow ("Im erchatz," "Im etkashet") or as an oath ("Im lo erchatz," "Im lo etkashet"). Rabbi Yosi disagrees and holds that these vows contain no affliction, since they amount to no more than refraining for a single day, but even according to him the husband can annul them under the category of "matters between him and her" - an annulment that is effective only as long as she is married to him, unlike the annulment of vows of affliction, which are annulled with respect to everyone.